question:  Why does the Scorpion leave their signature at each crime?
context: CALL HIM NEMESIS By DONALD E. WESTLAKE Criminals, beware; the Scorpion is on your trail! There was Mr. Featherhall at his desk, refusing to okay a personal check from a perfect stranger. There were Miss English and Miss Philicoff, the girls in the gilded teller cages. There was Charlie Casale, getting ten dollars dimes, six dollars nickels and four dollars pennies for his father in the grocery store down the street. There was Mrs. Dolly Daniels, withdrawing money from her savings account again. The three bank robbers looked like triplets. The third one, who carried a black satchel like a doctor's bag, walked quickly around behind the teller's counter and started filling it with money. The man who had first spoken herded the tellers, Mr. Featherhall and the customers all over against the back wall, while the second man stayed next to Mr. Anderson and the door. She fell unconscious to the floor, and all three of them ran out of the bank to the car out front, in which sat a very nervous-looking fourth man, gunning the engine. Two police cars came driving down the block and a half from the precinct house to the bank, and the car with the four robbers in it lurched away from the curb and drove straight down the street toward the police station. "What I can't figure out," said Stevenson, "is exactly what made those tires do that. Except that in the trunk lid the owner had burned in 'The Scorpion' in big black letters you could see half a block away." "If I'm making just a quick stop—I never spend more than five minutes with any one customer—I always leave the keys in the car. "It was four professional criminals, I thought you knew that. Stevenson followed Hastings' pointing finger, and saw again the crudely-lettered words, "The Scorpion" burned black into the paint of the trunk lid.
output:  To show that they "took care" of each criminal.
options:  To show that they "took care" of each criminal.  To scare off other potential criminals.  To show that they were present at the crime.  To help lead the police in connecting the crimes.