What is "handkerchief code"

n. A set of colors of handkerchief that indicate sexual preferences of people who deliberately wear them for this purpose.

The handkerchief code (also known as the hanky code, the bandana code, and flagging) is a color-coded system, employed usually among the gay male casual-sex seekers or BDSM practitioners in the United States, Canada, Australia and Europe, to indicate preferred sexual fetishes, what kind of sex they are seeking, and whether they are a top/ dominant or bottom/submissive. The hanky code was widely used in the 1970s by gay and bisexual men, and grew from there to include all genders and orientations.

Today, wearing color-coded handkerchiefs ( bandanas) is the manner in which communication of desires and fetishes is achieved. Wearing a handkerchief on the left side of the body typically indicates one is a "top" (one considered active in the practice of the fetish indicated by the color of the handkerchief), while wearing it on the right side of the body would indicate one is a "bottom" (one considered passive in the practice of the fetish indicated by the color of the handkerchief). This left-right reality is taken from the earlier practice of tops wearing their keys on the left belt loop and bottoms on the right to indicate being a member of the leather subculture. Bandanas might be worn in the front or back pocket, tied around the neck (with the knot positioned on either the left or right side); around the ankle (when wearing boots or when undressed); or on other parts of the body.

There is no universally understood color code, and regional codes vary widely. There is general agreement upon the colors for more common practices, particularly those with an intuitive relation between the color and the practice, such as yellow for urolagnia; brown for coprophilia; and black for SM, but no absolute consensus for less common practices.