Green’s Dictionary of Slang

(bingo) the number four.

1930		(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier.
1960		J. Franklyn Dict. Rhy. Sl.
1980		T. McClenaghan Submariners I ii: All the fours. spider: Pompey whores.
2001		J. Burkardt ‘The Bingo Code’ Wordplay 🌐 24: Pompey whore.