This is a bit of what I know about the hanky code, a sartorial semiotic approach to cruising for gay sex that went out of style 30 or 40 years ago. Yellow means you’re into water sports, red signals an interest in fisting, robin’s egg blue pertains to 69ing, mauve is for navel fetishes, union jacks are for skinheads, black, of course, advertises BDSM.