Green’s Dictionary of Slang

dinky-doo n.

(bingo) the number 22.

[UK](con. WWI) Fraser & Gibbons Soldier and Sailor Words 122: 22, ‘Dinky Doo’.
[UK]J. Franklyn Dict. of Rhy. Sl.
[UK]J. Jones Rhy. Cockney Sl.
[UK]P. Wright Cockney Dialect and Sl. 109: 22 = dinky-do.