The Sock on the Door, the Hanky Code and Other Secret Sex Signals

Some sex signals are private jokes between two roommates. Others were a whole language. A sock on the door handle tells the person you share a room with to find somewhere else to sleep tonight. A coloured handkerchief in a back pocket told gay men in the 1970s what someone was into, and the pocket told them which side of it. Before the handkerchiefs there were keys, and in the age of the text message there is "Netflix and chill".

Here is what each one means, where it came from, and how much of it still holds.

A sock hung on the outside door handle of a shared room means someone is inside with company and does not want to be walked in on. It is a student-housing custom above all: college papers have been writing about it for years. Stanford's student paper put it bluntly in 2010: "There's only one reason for a strategically placed sock on the door handle — you've been sexiled."

Sexiled, sex plus exiled, is the word for the roommate left standing in the corridor. Penn's student paper called the sock "the warning sock" the same year. The etiquette has not changed much: if you see one, at least knock, and if you hang one, a text to warn your roommate is the courteous version.

Before handkerchiefs, gay men used a simpler signal: a bunch of keys worn on the left or right side, to show whether they preferred to top or to bottom. It carried one piece of information, which is the problem the hanky code set out to solve.

The hanky code, also called flagging, used the colour of a handkerchief or bandana in a back pocket to say what someone was into. Its modern use is usually dated to the early 1970s, when a Village Voice writer joked that coloured handkerchiefs could signal more specific interests than keys ever could. By 1980 Bob Damron's Address Book was printing a version of the code.

The pocket mattered as much as the colour. Left usually meant the giving or topping side, right the receiving or bottoming side. The most widely followed colour list comes from the 1983 second edition of Larry Townsend's The Leatherman's Handbook II:

There was never a single official version, and lists disagree on the rarer colours. Everyday use waned in the early 1980s. Some leathermen still flag, and some parties and events use the code in a knowing, retro way. If you want to see where that scene lives now, our guide to gay cruising clubs in Berlin is a good place to start.

The newest code on this list is a phrase. Merriam-Webster records Netflix and chill as an informal euphemism for a casual sexual encounter at someone's home, and dates its first known use in that sense to 2015. Like the sock, it works because it has an innocent reading: you can always claim you really did just want to watch something.

The cruise-ship pineapple belongs in the same family, as a signal hiding in plain sight. We cover it, pampas grass and the black ring in the upside-down pineapple and other swinger signals.