Green’s Dictionary of Slang

Alice (Blue Gown) n.

also Miss Alice
[song ‘My Sweet Little Alice Blue Gown’ by McCarthy & Tierney (1918); thus the ref. is to the uniform]

(US gay) the police.

R.A. Farrell ‘Argot of the Homosexual Subculture’ in Anthropological Linguistics 98: ALICE (n.): The police (syn. BLUE GOWN, FUZZ, LILLY LAW, MAGGIE, TILLIE).
[US]B. Rodgers Queens’ Vernacular 125: the police Alice [...] Alice Blue gown [...] Miss Alice.
[US]Russo ‘Camp’ in Levine Gay Men (1979) 206: Police become ‘Alice blue gown’ or ‘Tillie law’.
[US]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).
[US] (ref. to 1944) A. Bérubé Coming Out Under Fire 86: A policeman was Alice Blue Gown.
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.
(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.
[NZ](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.