The White Hand Gang was a coalition of Irish street gangs in Brooklyn known for terrorizing Italian immigrants. Even among New York criminals they were notorious for liberal use of violence, lynching dozens of Italians along the waterfront. The White Hand Gang’s reign of terror ended in 1924 after a violent confrontation with a young Al Capone at a waterfront bar.
Sources:
Capone: The Man and the Era by Laurence Bergreen
Five Families: The Rise, Decline and Resurgence of America's Most Powerful Mafia Empires by Selwyn Raab
American Mafia: The History of its Rise to Power by Thomas Repetto