The black hand is a favorite image of many groups. Easy to create and, before the age of finger printing, hard to trace.
Another way this symbol has been used was by the early Mafia groups in the United States. The black hand was a handprint on a piece of paper that would be left to intimidate extortion victims. It let them know that they were marked for death by the one of the gangs that were the predecessors to the more organized La Cosa Nostra groups. It was used from about the turn of the century until the 1920's as the gangs grew into organized crime rings.
It had started in Sicily during the 1700's. Pictures of a black hand were distributed to the wealthy. This was an unspoken request for an amount of money in return for protection. If the money wasn't paid, the recipients could expect violence such as kidnappings, bombings, and murder. In contrast when it arrived in New York it was mainly against the poor immigrants, those that would not go to the police out of fear or lack of knowledge.