Prowler RED Orange Hanky. Flagging is a color-coded system used in the gay community and the BDSM community. Colorful handkerchiefs are worn to indicate what sexual kink the person wearing it is into. When worn on the left side, the person is a top (active), and when worn on the right, they are a bottom (passive). The Hanky code became popular in the 1970s, allowing people to discreetly showcase their sexual preferences in nightlife.