12 · noun1
Of uncertain origin. Widespread use of the phrase as an anti-police slogan grew following the 2014 killing of Michael Brown in Ferguson, Missouri. * Possibly from 1312, an alternative form of ACAB (“all cops are bastards”) in which the letters are substituted with their position in the alphabet. * Alternatively, from the American police procedural television series Adam-12 (1968–1975), in which 1-Adam-12 refers to a patrol unit and its radio call sign. Likely popularized by "F*ck 12", a song by American hip-hop group Migos from their 2013 mixtape Y.R.N. (Young Rich Niggas), which uses 12 in reference to the police while describing a narcotics raid: “12 kickin' in my front door […] 12 in my home, they won't leave me alone”.
12 · noun2
Shortening.
12 · symbol3
The alphanumeric code for AB, an initialism for the Aryan Brotherhood.
Etymology from Wiktionary, CC BY-SA 4.0.