Black Hand, common name in the United States for an offshoot of two long-established societies of an intricate and powerful order of Italian criminals, known in their respective strongholds of Naples and Sicily as the "Camorra" and "Mafia." The habit of the members of signing blackmail and threatening letters with the words "black-hand," or a rude representation of one, gave these desperadoes in the United States their distinctive name.
Entry from Everybody's Cyclopedia, 1912.