via VITAL VOICE
“At the start when the police would come into the bar the kids would yell, “switch” because the boys were dancing with boys and then the boys would grab a girl,” she explained. “Then one night they [the police] came in and somebody yelled “switch” and all of the sudden he [the officer] took his nightstick and slid it down to the floor and said, “Carry on kids.” And we did ever since.”
http://www.thevitalvoice.com/lifestyle/51-1-out-of-10/317-springfields-smokeys-den