16th Street at Bryant, San Francisco. This sign (or signs) has been here for years, just behind The Double Play bar. I'll dig up the story behind them -- there's at least one similar art piece on 6th Street, south of Market -- at some later date.
[That later date is now: KQED friend and colleague Molly Samuel advises they're by a San Francisco artist who goes by the handle Rigo 23 (if Wikipedia is to be believed, his full name is Ricardo Gouveia.) Thanks, Molly!]