Green’s Dictionary of Slang

Sidney rocks n.

also Charley rocks

[rhy. sl.]

(US) socks.

1920		T.A. Dorgan in Zwilling TAD Lex. (1993) 128: Sidney Rocks, that’s socks.
1935		A.J. Pollock Und. Speaks 20/1: Charley Rocks, socks.