Greg, it might be the font used for the denomination. I used it for posters and sign designs in the mid to late 70's. The font artist was Arnold Bocklin (not sure of the spelling of his last name, its been a while). Peter Max never blended colors, they were always VERY stark contrasts.

This is one of the things that has attracted be to this hobby. The graphics integrated into these tiny treasures are true works of art!

Bob