Handkerchief code, more commonly known as hanky code, was a way of indicating, usually among gay and gay Leather casual sex seekers or BDSM practitioners in the US and Canada, whether they were a top or bottom, and what kind of sex they were seeking, by wearing colour-coded handkerchiefs (or some other piece of material), usually in the back pocket of jeans. These were worn on the left side of the body for tops and the right for bottoms (this division is still somewhat common: tops may wear keys on the left belt loop and bottoms on the right, for example).
There is no universally understood colour code, and there may have been regional variations. There is, however, a general agreement on the colours for more common practices: yellow for watersports, red for fisting, navy for anal intercourse and black for generalised S&M, as well as brown for scat, but there was no consensus for the more uncommon practices, mainly because of the difficulty in acquiring such coloured handkerchiefs, but particularly because no one save for a gay sex shop clerk ever bothered to learn them all.
It is less common than it used to be, perhaps due to the advent of Internet dating and the coming out of more members of the leather and BDSM communities. For the universally understood colours, however, the basic hanky code still holds, and, for the totally out, is often a part of one's everyday street wear (but red hankies need to be further explicated before one makes a pass in non-gay contexts).
- Trevor Jacques, On the Safe Edge: A Manual for SM Play ISBN 1-895857-05-8
- Eric J. Trimmer, The Visual Dictionary of Sex (1978) ISBN 0 330 25890 7, pages 74-5