The artist is Terre, who is closely associated with Haight Ashbury’s Straight Theater, which is identified on the middle left of the map. The exotic fruit hanging from the various branches, as well as the mountains at the bottom of the ad, are direct allusions to Barbara Remington’s cover art for the first authorized paperback edition of The Lord of the Rings.
According to SFist, in 2013 the awning of a beauty salon was removed in North Beach, San Francisco, revealing a beautiful, hand-painted sign (below) of what was once a second Middle Earth Clothing location.
See also A Change of Hobbit Bookstore.
2 Warps to Neptune 
Wonderful to see this lettering again. I am Nathan Terre’ the artist who made
The middle earth hand bill, this was in the “summer of love” 1967.
Now reside in Missoula Montana and will always remember the Haight
Ashbury of which every part I was most familar.