American and European street gangs have traditionally used tattoos to intimidate those who view them, show gang affiliation, and indicate rank. They can indicate who a gang member is, what he believes, what he has done, where he has been, where he was imprisoned and for how many years, as well as the number of people he has killed. The more police investigators know about the tattoos of particular gangs, the more information they can gain from specific tattoos of gang members under investigation or in custody. This article provides information on the tattoos of the following American Black gangs: the Black Guerilla Family; The Bloods; The Crips; The Kumi Nation, 415; and The Black Gangster Disciples. Information is also provided on the tattoos of the following Hispanic gangs: The Mexican Mafia and The Nuestra Familia. Tattoos of the following White gangs are described as well: The Aryan Brotherhood and the Nazi Low Riders. Some general techniques used by gang members to disguise the meanings of their tattoos are also briefly described.