Growing up in California in the 80s, the only time I saw that style of S is in graffiti. Perhaps some 60s psychedelic concert posters like from the Fillmore?
Edit:
Top left S (in Otis) from a Fillmore poster from 1967 for the Otis Rush/Grateful Dead. Not quite it because of the flattened top, but pretty darn close on the inner-lines. Or the “S” in Sun at the bottom two thirds if you rotate it counter-clockwise so the hump is on top.
