If you have a Telekinesis spell, the lowest-end one svcks btw, because it doesn't have the range.... but if you have one of these spells, equip it, and slowly, left to right and back again, "paint" your target with your crosshairs. On 360 if you do this, their name will flash at your crosshairs, telling you who or what that is.
Those adventurers are rare, however, I try to keep them alive... it's nice having a pleasant conversation with a fellow adventurer with dead bodies all over the place.