For example, a dark blue handkerchief indicates an interest in anal sex, and wearing it in the left pocket indicates a preference for being the penetrating partner.

Wearing a handkerchief on the left side of the body typically indicates one is a 'top' (considered active in the act/fetish indicated by the color of the handkerchief) while wearing it on the right side of the body would indicate one is a 'bottom' (considered passive in it).

The color of the handkerchief identifies a particular activity, and the pocket it is worn in (left or right) identifies the wearer's preferred role in that activity. The handkerchief code (also known as the hanky code, the bandana code, and flagging) is a system of color-coded cloth handkerchief or bandanas for non-verbally communicating one's interests in sexual activities and fetishes.