"They can feel the sense of power by outsmarting the police."
Signatures often help investigators — much like those in the smiley face case — to link several crimes together and, more than anything, to establish a dialogue between authorities and perpetrators, that can often be helpful in solving these crimes.
"Any information investigators can obtain may suggest that there's a possible inroad to who might be doing this, or a lead," said N.G. Berrill, a forensic psychologist and director of the New York Center for Neuropsychology and Forensic Behavioral Science.
Of the smiley faces, Berrill said, "there's obviously some dialogue that's being established with these signatures, clues or symbols."
Many serial killers have historically reached out to the media for attention, said Berrill, notably Unabomber Ted Kaczynski, who sent a series of mail bombs, killing three and injuring 23 from the late 1970s to the mid 1990s.
"The idea is that some kind of dialogue will tantalize the authorities and provoke them or tease them," Berrill said. "It's not a cry for help, it's a cry for attention.
"These guys have no conscience," he added.