Marks? Or Legion Troops, Thomas?
The Khorne Lord joining a Plague Marine squad does NOT gain FNP (but I bet you knew that). If he joins a CSM squad waving a Stank Banner (i.e. Nurgle) for the T5, he *may* get that while he's with the squad ... not positive until I check the Codex. The rule of thumb is:
The Icon grants the squad "Modifier/Rule X".
All members of the squad gain "Modifier/Rule X".
Character joins aforementioned squad, he then gains "Modifier/rule X"
The first example that comes to mind is the Narthecium. A Narthecium grants Feel No Pain to the squad. Characters in the squad also gain Feel No Pain. Some other examples:
- Litanies of Hate
- Shrike's Infiltration
- Khan's Furious Charge/Hit and Run
- Snikrot's "Ambush"
... etc, etc
I think the Berserker's Furious Charge is a USR that carries an Asterisk on pg 74-ish (don't have my BRB on me) ... and is subsequently lost if joined by a unit that doesn't have the same USR ... The Lord would keep his T5, but he would not gain the Furious Charge. I'm also pretty certain that the 'Zerkers would lose Furious Charge while he's attached to them.
Damn not having my rulebooks. You'd think I'd have this memorized by now.
Jeff (herojones) is right about the "generic" marks. If you're talking about Chaos Space Marine squads with the Icon of "X": those are stat mods that do not grant special rules, and therefore are not affected by the dreaded "asterisk stigma".
Once again, no rulebooks on me at home, but I'll check for ya Monday. Tony can probably follow this up if he checks back before then (he's right in that anyone can join just about anyone in C:CSM) - it's simply a matter of what units you are asking about, and if the relevant USRs are kept or not.
Heck, call John if ya need to, he prolly has it memorized =P
Be well,
Dave