I remember a rocker/greaser living nearby in the sixties who had ACAB written in big silver studs on the back of his leather jacket- that was in Tottenham in London. He was what they used to call back then a "bus stop cowboy" - somebody who had all the greasers' gear - the boots , the greased back hair and jacket - except for the motorbike. The police picked him up one evening wearing the jacket at a bus stop outside the local greasers' caff , held him in a cell overnight and brought him to court next morning. He may just about possibly have got away with telling the magistrate that he bought the jacket second hand not knowing what the letters stood for . Instead he came out with some convoluted story about buying it second-hand thinking that ACAB stood for "All Canadians are Bums". The fact that the beak didn't believe him for one minute showed how well known the rhyme was back then