Just wanted to hear your opinion. Let's say Kill Team encounters Chaos Star symbol (eight arrows) - if nobody has Forbidden Lore do they identify it as a Chaos / Corrupt symbol?

Compared to the standard Imperial citizen, Space Marines are far better informed, and given that the Horus Heresy is one of, if not THE central tenet of their history, any Space Marine would know the eight-pointed star and also the Legion marks of the Traitors at the least.

An average space marine would easily be able to identify an overt chaos symbol as a chaos symbol. He would not, on the other hand, be able to identify the specific minor or obscure cult, or that cult's particular beliefs, these certain symbols represent. This is what forbiden lore would be used for. The symbols for the 4 main chaos gods and any chaos symbols specific to their chapter's history (from chapter lore) and just about any icon or symbol they've seen before (most marines develop photographic memories) they'd be able to easily recognise of course.

Just posting up a reply to put this recent discussion back where it belongs after all the necro posting by yibbo.

In my group we came to the agreement that all space marines should know about the traitor legions, their basic heraldry (IE 8 pointed star), and that they worship something other than the emporer. Without the forbiden lore skills, they do not understand about the demonic powers of the warp and their influence on the traitors