Green’s Dictionary of Slang

(gay) to reveal one’s sexual preferences by dropping broad hints; thus keep your hairpins up, maintain a ‘normal’ mask.

[1932		‘R. Scully’ Scarlet Pansy 214: One chubby-faced fat fireman put his hands on his hips, wiggled and let out a ‘Whoops-my dear!’ Another called, ‘Ella, you’re losing your hairpins’ and still another, ‘Kitty, you should wear your veil when you’re on the streets’].
1943		T. Williams letter 12 June Letters to D. Windham 77: The [...] service-men are out for blood—indiscriminately. [...] [A]ll the local girls [sc. gay men] have gone underground for the duration, speaking in whispers and dropping never a pin in public places [Simes:DLSS].
1964		Homosexuality & Citizenship in Florida 24: Glossary of Homosexual Terms [...] ‘hair pins’ or just ‘pins’: To drop hints to a person whose ways are unknown, to determine iof he is a homosexual or not .
1965		A. James America’s Homosexual Underground 142: Women who understand homosexuals are said to ‘know the score.’ They’re not supposed to be shocked by anything. So when they attend a party there’s no furtive whispering at the door. You don’t hear ‘Keep your hairpins up, dearies...There’s a “straight” inside.’.
1965		Guild Dict. Homosexual Terms 12: drop hairpins (v.): For a homosexual to hint about his inversion to another person in order to ascertain whether that person is also homosexual; to do this accidentally.
1966		J. Barr Occasional Man 196: The Baroness [a gay man] put a finger to David’s lips and said, in a horrified whisper, ‘For Heaven’s sake, David, don’t call me that in these clothes, and today in particular. Call me Theo or Tony. My wife’s in town with some of her Mid-wesstern relatives, and we don’t dare drop a pin’ [Simes:DLSS].
1970		J.P. Stanley ‘Homosexual Sl.’ in AS XLV:1/2 57: drop hairpins v Reveal one’s homosexuality by dropping hints.
1972		E. Newton Mother Camp 33: The process of sending out subtle cues or ‘feelers’ is called ‘dropping the hairpin.’ (This phrase is also used when one has made an outright admission of homosexuality).
c.1972		‘S. Chadwick’ Rough Trade 58: Rodney was trying to find out whether or not Tom was gay, and if so, what sort of sex he enjoyed. He was trying to get the answers without asking the questions, without dropping his own pins [Simes:DLSS].
1986–7		Maledicta IX 144: The effeminate ones (working girls) may drop a hairpin in conversation or otherwise advertise availability; this is called posting flyers.
1999		D. Lypchuk ‘A dirty little story’ in eye mag. 8 July 🌐 When she confronted him he suggested that she have a double peptide with his old saw, so she performed an orchidechtomy on him. After that she decided to drop her hairpins and show her true colours to the world.
2003		K. Cage Gayle 67/2: drop a hairpin v. give a subtle signal that one is gay [Western Cape, 1950s].
2009		(con. 1951) S. Estes Ask & Tell 42: He was a very, very nice gay, as gay as pink ink. He took me into San Diego that same evening and he dropped a few hairpins , which I didn’t pick up because I was too stupid .