Green’s Dictionary of Slang

(US gay) the police.

1972		R.A. Farrell ‘Argot of the Homosexual Subculture’ in Anthropological Linguistics 98: ALICE (n.): The police (syn. BLUE GOWN, FUZZ, LILLY LAW, MAGGIE, TILLIE).
1972		B. Rodgers Queens’ Vernacular 125: the police Alice [...] Alice Blue gown [...] Miss Alice.
1976		Russo ‘Camp’ in Levine Gay Men (1979) 206: Police become ‘Alice blue gown’ or ‘Tillie law’.
1980		Maledicta IV:2 (Winter) 230: Cops are also called Alice (song ‘Alice Blue Gown’, Bluebottle [...] Brenda Star(r) from the US comic strip (and their badges).
1990		(ref. to 1944) A. Bérubé Coming Out Under Fire 86: A policeman was Alice Blue Gown.
1997		Gay Today 27 Aug. 🌐 He’s off to seek an offender, without wearing his Alice Blue Gown / He won’t even display tin jewelry as he haunts every park in town. / His name is Percy Policeman; he’s a dear, sweet, handsome young man, / Who wags his privates at people, while he waits in the stink of the can.
2002		(con. 1930s) Rainbow Hist. Project (Wash. DC) 🌐 Gay friendly in the 20s and 30s, The Republic Gardens was a large restaurant-bar with a completely gay backroom [...] If a policeman walked in the door, the vocalist would let us know by Singing ‘Alice Blue Gown’ from the Broadway musical Irene. –Ladd Forrester.
2010		(con. 1960s) W. Ings ‘Trolling the Beat to Working the Soob’ in Int’l Jrnl Lexicog. 23:1 72: In the early 1960s in New Zealand Vivian Vice, Nelly-law, Dolly Handbag, Alice, Dora-D, Hilda-Handcuff, Lily-lunchbox, Jennifer-Justice, Hilda Box-rot, Petunia Pig, Tilly Tight-twat, and Cherie Cunstable, were familiar.