9.75x12.75" small size stiff paper poster for protest and concert event held on June 13, 1971, in the Grande Ballroom in Detroit, MI. The reason behind the concert was the arrest of John Sinclair, who was given a 10 years jail sentence for possessing two joints. Shortly after the event, Sinclair was released. Great poster design by Gary Grimshaw features Sinclair photo at top center, flanked by two marijuana leaves. Performers included - Assemblage, Frut, Guardian Angel, Brat and The Up, Grande Ballroom's house band. Poster has some minor handling wear, mostly to corners and top margin has been signed in blue ink "For Mark - Thanks John Sinclair" and bottom margin has also been signed in blue ink "Thanks Mark - Frank Bach." Bach was the vocalist for The Up. Bottom margin has also been signed in black felt tip pen by artist Gary Grimshaw. Faint 5" crease across performers' names but poster remains bright w/bold/strong color. Displays Exc. Scarce. From the Mark Arminski Archives and comes with a COA specially designed, signed and remarqued by him.