Sureños (Spanish for "Southerners"), or Sureñas for females, are groups of loosely affiliated gangs that pay tribute to the Mexican Mafia while in US Federal and State correctional facilities. Sureños use the number "13" which represents the thirteenth letter of the alphabet, the letter "M", in order to pay allegiance to the Mexican Mafia. Many Sureño gangs have rivalries with one another and the only time this rivalry is set aside is when they enter the prison system. Thus, fighting is common among different Sureño gangs even though they share the same common identity. This street gang is known for wearing the color blue and typically heavily covering themselves in tattoos to show affiliation. The Sureños main stronghold is in Southern California where they originated. There are an estimated 20,000 Sureños in Los Angeles County alone. They have successfully migrated into every major city in every state in the United States, as well as Canada, the US Military, Mexico, Honduras, El Salvador and Guatemala. One of the main reasons for this migration is due to California's harsh three strikes law. There are unconfirmed reports of their presence in various South American countries as well. Many larger criminal street gangs use the number 13 under the Sureño banner such as the 18th Street Gang and Mara Salvatrucha.