During the 1950s (and any time period for that matter), gangs would use graffiti to mark off their turf as a warning to enemy gangs. Unfortunately, pictures of gang graffiti are rare and hard to come by. But here is a nice picture of gang graffiti of a gang from East Harlem called the Dukes. The Dukes were an Italian gang who got into fights with the Dragons another gang from East Harlem.
The Dukes were involved in a gang shooting on June 11, 1956 against their rival Dragons, of which I hope to have more information later.
Many thanks to Enrique Caro who gave permission to use this picture, below you can make out the gang graffiti of “Ellery Bops,” a gang from the Williamsburg area in Brooklyn. You can also make out the letters LAMF which means “Like a Mother F__).