[ It's definitely not his area of expertise, but let him try and think of something... ]

Not really? They can't be seen by the naked eye, usually... unless they're possessing a corpse.

[ What else? ...oh, duh. ]

They also have a distinctive crimson aura, but you'd have to be a pretty high-level Caster or something equivalent to that to see it. I can't say I qualify, especially since I'm not even supposed to be a Caster...

Sorry if I wasn't much help, Mr. Cherryblod.