The story
From fuck + 12, of uncertain origin. * 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 mixtape Y.R.N. (Young Rich Niggas) (2013), which uses 12 in reference to the police while describing a narcotics raid. Widespread use of the phrase as an anti-police slogan grew following the killing of Michael Brown in 2014 in Ferguson, Missouri.
Etymology from Wiktionary, CC BY-SA 4.0.