Green’s Dictionary of Slang

the ‘utility’ mark, made of two capital Cs, meaning ‘civilian clothing’ plus the date of manufacture.

1974

(ref. to WWII) Illus. London News Oct. 28: The Utility sign; called in its day [WWII] ‘the cheeses’, this was two capital Cs, standing for civilian clothing, plus 41 for the year 1941 [DSUE].