Take a look at this poster known as "the Brain". Check out how the brain matter spells: POT in the center. It promotes gigs dated 12/8-10/67 at the Vulcan Gas Company by 13th Floor Elevators, Shiva's Head Band, Canadian Overflow & Swiss Movement.
This poster has some tearing along the edges but is still very valuable. These full-sized Vulcan posters were only printed in lots on 100 and so not many of them survive.