Book of shadows: Death Grimace

The caster marks a corpse with a particular magical “signature," thus identifying himself (truthfully or falsely) as the murderer. Some assassins use this signature as a sort of calling card, while others use it as a way to prove that they earned their pay. The signature can take many forms: a specific expression on the face of the corpse (hence the name of the spell), an actual rune, a word written on the corpse’s flesh, a discoloration of one eye, and so on.