1989 Signed Mark McGwire Oakland A’s Mother's Cookies Card Advertising Display Sign / Poster.  See Photos as it has a JSA Certification letter along with the original invoice from EAC Galleries that Sold the item in auction

Mark signed the poster very boldly in black felt tip pen. 

This Bright and colorful 18" x 18" cardboard advertising display sign / Poster promoting Mark McGuire Baseball cards that could be found in Mother's Cookies bags and box’s (on specially-marked packages of the company's product).  In just his third full season, McGwire was a fan favorite in 1989, having led the league in home runs his rookie year of 1987 with 49, and followed up with 32.  The Athletics would finish the season 99-63, and sweep the crosstown Giants in the World Series.

The sign presents well, but does exhibit some corner wear and light creasing as can be seen in the photo.  Rare Store Display Sign that could only be obtained on the West Coast, so its very rare.