The Aryan Brotherhood is the oldest and most notorious racist prison gang in the United States, having started in California in the 1960s. It is present primarily in the California and federal prison systems. Many other prison gangs now also use "Aryan Brotherhood" as part of their name, such as the Aryan Brotherhood of Texas, but they are independent and unrelated to the "original" Aryan Brotherhood.
Because of its longevity, Aryan Brotherhood members have come to use a variety of symbols and codes, but the most common symbol of the Aryan Brotherhood remains a shamrock, often in combination with a swastika. Aryan Brotherhood members also frequently use the initials AB or their alphanumeric equivalent of 1 and 2, or 12 (including the use of Roman numerals). Another fairly common signifier is the use of the number 666 (the so-called "number of the beast").