The hanky code is a system of color-coded handkerchiefs typically used by gay men and members of the BDSM community seeking casual sex. Those who follow the code wear a hanky to show their sexual preferences. This practice originated among gay and bisexual men in the 1970s. Today, the hanky code is used by people of all genders and sexual orientations throughout the United States, Canada, and Europe. The Hanky Code is short for the handkerchief code. It is also known as the bandana code and flagging.

Wearing a handkerchief of a particular color on a particular part of the body helps communicate your sexual preferences to the people around you. For example, tops wear their handkerchiefs on the left side of their bodies while bottoms wear their handkerchiefs on the right. Color coding can vary from region to region, but there are some practices that are typically associated with particular colors. For example, a yellow handkerchief generally represents an interest in urolagnia, a brown handkerchief demonstrates an interest in coprophilia, and a black handkerchief typically communicates an interest in sadomasochism. Traditionally, color and placement of a hanky were the only important elements, but in some communities a handkerchief's print and fabric are also considered significant.

Handkerchiefs are often worn in a person’s pocket, around their ankle or wrist, around their thigh, or tied around their neck with the knot to one side or the other. If the hanky is worn on the back, in the center belt loop, it shows that someone is sexually versatile. A set of keys can be worn the same way as handkerchiefs to indicate whether someone is dominant, submissive, or versatile.

The hanky code was very visible during the 70s and early 80s, but waned in popularity in recent decades due to the increased visibility of gay people and the rise of AIDS. To avoid confusion, many people like to wear two handkerchiefs to show that they are indicating a sexual preference rather than making an innocent fashion choice. Despite falling out of favor, the hanky code can still be a useful way to communicate sexual preferences in noisy bars and a great conversation starter for those in the know. As colors can look different in the dim lighting of a bar or club, it’s important to verbally confirm the information you believe the hanky is signifying before engaging in any scene.