I have occasionally heard people describe promiscuous young women as "the town bicycle." The joke being that, like a communal bicycle, everyone gets a ride (i.e. sex).
However, I have never actually been to a town which has a town bicycle, and I'm not entirely sure how it would work. I picture the intersection of Main Street and Lincoln, Anytown, U.S.A. There is an island in the middle of the road, with flowers and a statue of someone important, or perhaps a veterans' memorial. At the base of the statue sits a lone Huffy ten-speed. The sign above it reads "Town Bicycle - Please return it when you are done." Alternatively, the bicycle may be available for check-out at the local library.
Sadly, liability concerns have forced the town to consider abandoning the town bicycle scheme. But it was a glorious tradition while it lasted.