The handkerchief code is a system of color-coded cloth handkerchief or bandanas for non-verbally communicating one's interests in sexual activities and fetishes. The color of the handkerchief identifies a particular activity, and the pocket it is worn in identifies the wearer's preferred role in that activity. Wearing a handkerchief on the left side of the body typically indicates one is a "top" while wearing it on the right side of the body would indicate one is a "bottom". 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. The code was first used in the 1970s in the United States, Canada, Australia, and Europe, by gay and bisexual men seeking casual sex or BDSM practitioners. Over time the colors and types of apparel in use have greatly proliferated.

A handkerchief is a form of a kerchief or bandanna, typically a hemmed square of thin fabric which can be carried in the pocket or handbag for personal hygiene purposes such as wiping one's hands or face, or blowing one's nose. A handkerchief is also sometimes used as a purely decorative accessory in the breast pocket of a suit; it can then be called a pocket square. A handkerchief is also an important accessory in many folk-dances in many regions like the Balkans and the Middle East; an example of a folk-dance featuring handkerchiefs is the Greek Kalamatianós.