Okay, so the talent indistinguishable says something like "Increase the difficulty of someone to identify the character one step per rank of indistinguishable" - but then it occurs to me that there's no actual mechanic (or really any guidelines) on how to identity people anywhere in the book(s) - at least that I've found. Or did two pages of my book get stuck together and I just never noticed?

What is the customs inspector rolling? Perception, probably? Perhaps Core Worlds if they're trying to identify a Hot Young Starlet? What's the difficulty range at? Presumably someone who looks like the Elephant Man or Mister Bean would be pretty easy to pick out of a crowd while a skinny black man at a Skinny Black Man convention would be significantly harder.

How do you guys handle this shockingly vague mechanic?

Okay, so the talent indistinguishable says something like "Increase the difficulty of someone to identify the character one step per rank of indistinguishable" - but then it occurs to me that there's no actual mechanic (or really any guidelines) on how to identity people anywhere in the book(s) - at least that I've found. Or did two pages of my book get stuck together and I just never noticed?

What is the customs inspector rolling? Perception, probably? Perhaps Core Worlds if they're trying to identify a Hot Young Starlet? What's the difficulty range at? Presumably someone who looks like the Elephant Man or Mister Bean would be pretty easy to pick out of a crowd while a skinny black man at a Skinny Black Man convention would be significantly harder.

How do you guys handle this shockingly vague mechanic?

I think it is usually going to be Perception, though I'd also see cases where it could be Streetwise or even Skulduggery, depending on the variables or the PC's methodology.

As for the difficulty, I'd assign it on a case by case basis as appropriate and then simply +1/rank as indicated by the talent.

Look under the perception skill. Second paragraph from the end. Advantage may be spent to recall additional information associated with the object noticed. So on a perception check to notice the character you upgrade the difficulty. Thus lowering the chance of getting advantage to spend on recalling additional information.