To the best of my knowledge, there was some throwaway exposition about someone's specific aura being unique to them that persists across transformations, so you can't just pop a potion and escape law enforcement after dine and dashing from the local Greggs. Out in the rural areas and away from any real authority: anyone who can't perceive auras probably gets fucked over by them... although a part of my brain is reminding me it might be just subconscious, even without any sensitivity to magic, so it doesn't actually matter, i.e. you just "know" it's someone despite their new appearance?? I don't really remember, though, and I'm not willing to boot up the game to find out.