A signature is an aspect(s) of a crime that is completely unique to the perpetrator(s) and commonly not shared by any other. It is also known as a signature crime, signature aspect, signature behavior, or signature characteristic. It is not to be confused with the term "modus operandi", which details the exact crime(s) committed. Signatures fulfill a psychological need for the perpetrator(s) and often do not change in the commission of their crimes.
John Douglas names two typical examples of a signature in his book Crime Classification Manual:
- A bank robber in Grand Rapids, Michigan, forced his hostages to undress during a robbery and took photos of them before taking the money.
- A rapist forced the victim's husband to return home and be humiliated by the crime.
The so-called "Gatton Tragedy" also involved a notable signature. After they were killed, the victims' legs were positioned in a way that they crossed over their bodies, with the feet pointing westward.