By not wearing helmets or by the personal heraldry/totems/wards/etc. etc. that sets each of us apart.
Go ask that question of people who care; maybe then you'll get an actual answer. Edit: They'll all be dead, after all.
Last time alpha legion tried infiltrating the spacewolves. (And now im gonna qoute BL) Bjorn massacred them. this was also the last time aplha legion thought the wolves could be infiltrated like the others. (srry, will be drunk next time. promise)
i have no idea i would kill the imposter damned basted he would be we look less identiacal than necrons (also the the thing that Vlka fenryka rarely wear helmets. me like hte art. they get surgery to look more alike even under the helmet. also their primarchs are the smallest spacewolves look like this before they become spacemarines. who do you think Fenris be da best place for that in 40k. (rl be some slavic placeees)
How cold is a space wolves smile? Whats the longest a space wolves has been away from his chapter and return to tell the tail about it?