Serial murders tend to share a number of common characteristics. Anger, low self-esteem, fantasy, facilitation, and objectification of victims are all common factors in understanding the general etiological roots of serial murder. Some cases, however, have distinctive behaviours that make the crime and the offender(s) unique. These are referred to as the signature or personal marking, of the offender. Signatures include verbal, sexual and physical acts. For example, most cases of serial murder are described in terms of patterns of murder customised to fit the special needs and fantasies of each killer. The signatures are also referred to as ‘calling cards’ or ‘trade marks’ and can be used by repeated violent offenders who are not serial killers. For example, a serial rapist may demand that their victim beg for mercy or tell them they are enjoying the assault.
The MO, or Method of Operating, is separate from motive and signature. MO includes techniques to commit the crimes, which may evolve as the offender becomes more experienced and skilled. Signatures are actions of the serial offender usually unnecessary to completing the murders. There are exceptions, such as the case of Cary Stayner (pictured above) who enjoyed decapitating female victims. Such signatures are extensions of paraphilic fantasies and can facilitate the offender in actualising his fantasies.