Green’s Dictionary of Slang

(US) a moustache.

1940		D. Maurer Big Con 123: He had a little red stash, and he pulled it all out.
1972		B. Rodgers Queens’ Vernacular.
1982		Akron Beacon Jrnl (OH) 11 Aug. 42/6: LOST, male cat, black and white, marked with black moustache, ‘Stashie’.
1994		Montana Standard (Butte, MT) 30 Oct. 21/1: Barn cats [...] T.J. and ‘Stash’ (short for Moustache).
2000		Age (Melbourne) 20 Feb. 70/1: The newspaper made a case for the ‘stash’ by citing [...] mustachioed Ukranian model Eugene Hutz.