According to Jay Lynch, one of the original Topps Artists,  the initial on this Mod Generation Sticker artwork isn't an artist's signature, but Woody Gelman's 'mark', indicating it passed his approval.  Woody was the head of the creative department at that time.  

I've just been in contact with an artist from San Francisco who actually worked on this elusive set by the name of Trina Robbins. "I'm pretty positive that I drew that for Topps' sticker set back in 1968 or 69.  Designing that sticker set is the only work I ever did for them."

Also, in contrast to David Saunders information on his website Trina also says "They were NOT "designed and painted by Norm Saunders," they were designed by me and redrawn by him to fit Topps' more conservative standards. (He was a very sweet guy and told me he was sorry that he had to redraw them, said my originals were better.) At least, most of them are by me."

You can check out Ms. Robbins work from her website

Thanks for your help, Trina!!!