Green’s Dictionary of Slang

a two-note whistle aimed at a passing woman by an admiring, lustful man; or vice versa, see cit. 1953.

1945		Dly Telegraph (Sydney) 11 Aug. 13/2: [US source] Juicers and best boys and camera-men, and even make-up men, gave the wolf-whistle.
1946		Miami Dly News-Record (OK) 11 Sept. 6/4: The South American [...] wouldn’t demonstrate his Hollywood-and-Vine wolf-whistle.
1952		(con. 1944) Wilder & Blum Stalag 17 [film script] 24: Some give out cat-calls and wolf-whistles.
1953		W. Harrison Army Girl (1962) 60: Dan was just stepping into his trousers. Maxine gave a wolf-whistle.
1959		‘Monroe Fry’ Sex, Vice & Business 90: [used to indicate distance] The town's main street is a wolf's whistle away from the customs gates.
1961		R.S. Close With Hooves of Brass 75: [H]e stopped short and gave a long wolf-whistle.
1966		Statesville Record (NC) 20 Dec. 8/3: Wolf whistles may be either insulting or complimentary.
1977		Shreveport Jrnl (LA) 9 Dec. 10D/1: Women’s reactions to wolf-whistles, ogling and lewd remarks [...] vary.
1981		T. Wilkinson Down and Out 60: A man a few beds to my right attempted a kind of wolf-whistle.
1991		B. Quinn Smokey Hollow 66: The wolf whistles from men digging a trench.
2001		Guardian G2 20 Mar. 8: Good, I’m in sensory overdrive – blinding lights, wolf whistles, heart thumping.
2010		Vancouver Sun (BC) 2 Oct. E19/2: [cartoon caption] ‘Wolf whistle at your wife? Don’t be ridiculous!’.
2010		Honolulu Star-Advertiser (HI) 29 Oct. 10/1: New York looks at halt to wolf whistles.
2018		Ottowa Citizen (Ontario) 29 Aug. NP5/3: A woman who objected to him harassing her with wolf whistles.