Which came first, R Crumb's "Keep on Truckin'" illustration or The Grateful Dead song? I don't really know but the Internet does: answer. I do remember buying R. Crumb comic books and seeing his illustrations used for a variety of purposes on dorm room, coffee house (they used to be called that), and record store walls.
My friend, Rick, who sent this card, is a talented comic illustrator, and every year sends out an annual calendar using his illustrations to chronicle the highlights of his family's year. Kinda like a Christmas letter, only better.