Originated way before the punk & Oi appropriation of the abbreviation. References to it go back to the 1940s in the UK. Often as a tattoo on those who've had unpleasant dealings with the British police.
Occasionally seen as tattoo on the forehead during the punk/Oi era.
All Coppers Are Bastards / All Cops Are Bastards.
Origionally used by strikers in the UK, spread to prison inmates who often tattoo'd ACAB on themselves.
In the 70's became popular in the punk/oi scenes after the band 4-Skins used it as the title for a song.
Alternative defenitions are often used to avoid getting in trouble when quized on its mening, for example a march in germany had a banner proclaiming All Communists Are Beautiful.
2. ACAB - Anti Cuts Action Bristol, a local campaigning group fighting against austerity cuts and their root causes; capitalism and hierarchy.
3. Association of Community Access Broadcasters, a group of New Zealand community radio stations.
ACAB - Not from a bunch of white power twats, not from california.