Warrents of Trade have evolved over the centuries and not all are created equal.
It is one to three pieces of paper (extreemly valuable ones may be signed by the God Emperor himself) which makes several refrences to other legal documents.
e.g. Ensuring the loyalty and saftey of all plantes outlined in "Planetary Management and Responsibilities Contract 9182631" as well as fulfilling all other responsibilities of said contract.
This way you can be vague on the paper you supply your party with while making up responsibilities (endevours) for the 'planetary management' as the game progresses.

Warrents issued much more recently are tied to a specific person and even their own children would need to apply for a new warrent, to take over the dynasty, should the owner no longer be able to fulfill his duties.

'Into the Storm' has a whole 'Warrent Path' section, including differences for which 'Age' the Warrent was issued during. The book is worth getting as it adds tonnes of content.

'The Death of Augustus Killian' on page 15 of 'The Koronus Bestiary' paints a picture of a warrent of trade small enough to be carried on the Rogue Traders belt but also that many people have died trying to recover the warrent, "which would allow them to establish their own dynasty" (quote from mentioned chapter)

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It is one to three pieces of paper (extreemly valuable ones may be signed by the God Emperor himself) which makes several refrences to other legal documents.

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It's not always papers my friend. Though I do like your idea that the Warrant wil refer to other clauses in other documents for reference in certain matters. Makes it that much for easier for the Imperial Administrators to sneak something in there for future ploys/favors/demands/endeavors.

I haven't seen any set guidelines on how a Warrant is specifically written/documented within the Imperial. Just as you and everyone else mentioned, it changes year to year, Sector to Sector, Warrant Issuer to Warrant Issuer. Anyhoot, Happy Gaming people.

OLD warrants, some of which were signed by the Emperor, offer huge liberties to the RT with very few limits. Newer warrants are likely to have a thousand different clauses and limits to it.

The one fun thing about the warrant in my opinion is the variety of reasons why someone could get one. Some may have spent their life building up power and gaining favours to get the warrant. In some cases it might have been their family that strived slowly to gain power with the purpose of having one of their children be in position of gaining the warrant. For others it is an punishment...

Person X got too powerful in an organisation (inquisition, the church or navy/guard perhaps even administratum) so the warrant is given out as a way to eliminate them from the power struggle. In the guard for example, by the time someone can be considered as a contender for the position of warmaster they hold huge powers already. Besides, in a Warmaster vs Rogue Trader power comparison the RT is likely to lose in all but their amount of personal liberties.

Also I think somewhere in RT rulebook it is mentioned that the children of an RT are likely to be sent to the guard to serve as soldiers to gain the experience they need when they are older. You would assume that this means that they get a position in some generals staff or at least start out from the officer school but perhaps the RT wanted to get their child started out in the school of hard knocks. Or maybe daddy just didn't like the spoiled bastard and that is why he got sent into the 32nd Dugistan "mines tompers" as an regular guardsman. Then at some point he hears the sad news about the loss of their parent as well as of their older siblings (Perhaps someone used too much poison in an attempt to gain control of their dynasty?) and they get the warrant.

I would think that Children of a Rogue Trader would be more likely to either go to the Schola Progenium / Officer School OR just serve long enough in the household armed forces of the family that they could make a name for themselves. But I can't see a rogue trader sending their ACTUAL heir apparent to the Imperial Guard, they are WAY too likely to die or go missing...

On the other hand, a classic character background would be something like

"Lt von Slinkoff, do you know why I called you here today?"

"Sir no sir!"

"Well, given the circumstances, I think we can dispence with some of the formalities lieutenant. Were you close to you uncle Alexandr?"

"Uncle Sasha? No sir, not really. He's a rogue trader. Married to my father's sister. Political marriage I believe. Only met him twice I believe. Can I ask why sir? Is there a problem with uncle Sasha?"

"Ah. Your uncle ... Sasha ... has died. With all of his closest family. And left you his Warrent of Trade. My orders are to get you safely to what remains of your family's ships. Also, you are hereby relieved of your commission."

"But sir! What about the enemy?!"

"Sorry, you've just been declared a higher priority. And please forget about the sirs. Oh, and while I have you here m'lord, could I perhaps enter a plea for the use of your ships to bombard our enemies from orbit m'lord?"

After all, a rogue trader is a peer of the Imperium. A mere imp guard colonel is (typically) not.

On the other hand, a classic character background would be something like

"Lt von Slinkoff, do you know why I called you here today?"

"Sir no sir!"

"Well, given the circumstances, I think we can dispence with some of the formalities lieutenant. Were you close to you uncle Alexandr?"

"Uncle Sasha? No sir, not really. He's a rogue trader. Married to my father's sister. Political marriage I believe. Only met him twice I believe. Can I ask why sir? Is there a problem with uncle Sasha?"

"Ah. Your uncle ... Sasha ... has died. With all of his closest family. And left you his Warrent of Trade. My orders are to get you safely to what remains of your family's ships. Also, you are hereby relieved of your commission."

"But sir! What about the enemy?!"

"Sorry, you've just been declared a higher priority. And please forget about the sirs. Oh, and while I have you here m'lord, could I perhaps enter a plea for the use of your ships to bombard our enemies from orbit m'lord?"

After all, a rogue trader is a peer of the Imperium. A mere imp guard colonel is (typically) not.

This seems more-than-less the backstory of Lord-Admiral Bastille the Seventh, who is one of my favourite Rogue Traders from the setting.

I think Imperial Navy is more likely than Guard but either way it's possible. I think in the above setting the Colonel might also apply for a job though!

It was actually quite close to the backstory of a RT (Homeworld: Battlefleet) that I wrote very soon after ItS came out.

Never did get to play that character though.

I think that a variety of answers is correct depending on the sector and the availability of the Warrant itself. Some dynasties store theirs in stasis on vault worlds, some carry them in their pockets in stasis containers. Note that the oldest Warrants signed by the Emperor can probably be verified by any Astropath, as his signature is supposed to be psychically identifiable. For more recent ones I imagine that you would need to convince the Administorium or Inquisition of the Sector of its validity. New sectors might only check with the old sector, or you might carry speically encoded messages from the previous sector.

For our latest campaign, I ran the obtaining and verification of the Warrant as part of the game. The Rogue Trader was the third son of a RT whom had been declared heretic by the Inquisition for helping the Tau convert a human world. The PC had been in service to the Imperial Guard for almost 20 years. He was captured and sanctioned by the Inquisition. Due to his record as an Imperial Guard general against both Chaos and Xenos some internal politics, he was declared innocent of heresy but the Warrant was handed off to a cousin anyways. While deployed on a passification campaign against a minor Chaos cult (only 5 regiments deployed) on a minor agro world, he came across a city based around an ancient ship partly burried in a hillside. The vaults of the ship included the Warrant of the now dead house that once owned the ship, signed with a drop of the Emperor's blood. The players arranged to sell the Teleportarium off the ship for sufficient funds and supplies to repair the ship and get it into orbit.

The campaign started with the players trying to get the ship repaired and lifted while investigating a mutant underground that ended up being a genestealer infestation. To make matters worse, the world had a hive ship from an long past Tyrannid fleet burried under the ice that the genestealer infestation had started to wake up. They had to juggle a Tyrannid infestation, the collapsing government of the world, the Imperial Guard survivors, and repairing the ship to try and get offworld. Help came in the form of an Inquisitor whose ship had been shot up in orbit by the local defense grid. They gathered and screened survivors, repaired the ship, got the ship to lift off, and used the ship's teleportarium to get to the Inquisitor's ship to launch a Exterminatus Torpedo at the world. It was an exciting little mini-campaign that ended up with the Inquisitor declaring the Warrant 'verified'. The documentation he provided and the 'verified' copy is how they prove their warrant. The original is locked in a armored vault in a Null Box. When they have to prove thier Warrant the present the 'verified' copy and the documentation from the Inquisition to the asking party.

A further note is that older Warrants have clauses that can cause a lot of problems. When you are required to spread the 'Imperial Truth' or to 'Suppress any and all religious organizations on worlds brought into Imperial Compliance', you need to do some fancy talking to show that you aren't going to cause problems for the Ecclesiastiary. Of course, you warrant doesn't even mention the Ecclesistiary...they didn't exist when it was written. Newer Warrants often include duties and tithes to whatever Imperial organization is behind the Warrant.

Personally, I have a few idea's for characters/campaigns I'd do if I could get the people around, and I have an idea how an everyman could get a Warrant of Trade.

Basically He was a rating on a voidship that did a great deed for the Imperium: saving the life of a Sector Governor, or maybe even a High-Lord. A Heretic Fleet tried to kidnap him, and the Navy, naturally, went to save him. It was the ship the Rogue-Trader to be was on that struck the killing blow and saved the VIP from the clutches of Heretics, but not without cost: a lance shot destroyed the command decks, leaving only the ratings behind. The VIP, wanting to thank his rescuer but finding him and his associates dead, decides to give it to one of the ratings, as they're the closest thing left. With so many, they hold a lottery to determine who gets it. And our Rogue Trader was the lucky winner!

I think that a variety of answers is correct depending on the sector and the availability of the Warrant itself. Some dynasties store theirs in stasis on vault worlds, some carry them in their pockets in stasis containers. Note that the oldest Warrants signed by the Emperor can probably be verified by any Astropath, as his signature is supposed to be psychically identifiable. For more recent ones I imagine that you would need to convince the Administorium or Inquisition of the Sector of its validity. New sectors might only check with the old sector, or you might carry speically encoded messages from the previous sector.

This. I think that it can just really depend - and verification of the PCs or even casting Aspersions against other NPC Rogue Trader's legitimacy could be useful.

I would just like to chime in that testing the credibility of a Rogue Trader can be a bit of a problem, and not lightly done. Sure, the Imperium may be a bureaucratic hellhole, but most bureaucrats do not have a death wish - and people know that a Rogue Trader is not one to mess with lightly. Now, a Rogue Trader may be validated by the warrant of trade, but s/he is also defined by being the master of a massive, heavily armed ship (or several) and in control of enough family resources and influence to keep this ship running, and then some. Most also have dynastic alliances and connections that span dozens sectors in the very least. Such people are usually considered to be eccentric, proud and often vindictive.

So, this raises the question - who the heck would be brave enough to try to mess with them, and with enough resources to have a chance? Inquisitors, the sector chiefs of the Arbites, perhaps, but anyone else would really rather avoid a confrontation, and even these would have to be careful. If there isn´t an Imperial Navy group on your side, you probably want to avoid making it a matter of life and death. Yes, a spaceport would want to know the ship and captain before it gives them docking rights (and most stations have the macrocannons to back it up), but a known ship or warrant would not be challenged lightly. It is one thing if your warrant has an explicit clause that you are forbidden from, say, sailing into or docking at the Segmentum Solar. It is completely another to show up at a faraway station in a sector bordering non-Imperial space. Sure, you may be expected to make a show of goodwill (bribes) if the ship name isn´t on any list, but that´s something any RT or seneschal worth their salt can do while asleep.

There was a bit in I think the core book that said that when people see someone descend from an armed voidship, walk around bedecked in ancient relics and exotic gear, surrounded by an extremely heavily armed personal guard, and claiming to be a Rogue Trader, they tend to take him or her at their word - because the alternative is usually worse.

That is also the issue with forging a warrant - without the ship and resources to back it up, it isn´t worth much. In fact, it makes you a very easy prey for the big boys and girls who do have the resources and would really like the warrant.

I would expect that the Imperial Navy, and likely the rest of the Adeptus Terra, would both maintain extensive databases at major posts and abridged versions on ships and more minor/distant posts and they would send out regular couriers with database updates.

The database updates would probably include a summary of those Warrants of Trade that are authorized or required to be active in their area of operations. They probably also include things like ships known to be attached to each Warrant, last known Bearer of the each Warrant, known pirate ships, etc.

Those databases would not necessarily be significantly up to date on events further out, but probably fairly current within the sector and adjacent areas, and the Navy would probably check for updates whenever they encountered another Navy ship or Imperial station.

That being said, unless someone is acting suspiciously and/or waving their Warrant (or specific clauses of their Warrant) around like a club to get what they want, it's likely that it will be assumed that they're what they say they are while they look and act the part, and no one will even bother checking (until/unless they make the right, or wrong, enemies). Navy ships are likely to be somewhat less trusting, but even they will usually only check to see if someone is a pirate or the like, not the legitimacy of the Warrant.