Green’s Dictionary of Slang

to shout ‘hello’, to attract someone’s attention.

1949		Wodehouse Mating Season 159: As I emerged into the station yard, somebody yoo-hooed.
1963		A. Baron Lowlife (2001) 200: Groups of boys and girls singing and yoo-hooing.
1963		‘Geoffrey Tolhurst’ Flat 4 King’s Cross (1966) 106: I did not recognise her at first, so far away those days seemed, almost another existence altogether. But she ‘Yoo—hoo’ed me’.