Firestone Super Sports Advertising Piece: Embossed Glass Ashtray in Tire

Description

Here is a very attractive advertising piece for Firestone.  This one is promoting the "Super Sports" model.
The piece is in great shape - rubber on the "tire" looks very good, nice heavy clear glass embossed ashtray. The only reason I don't call it excellent is because there are traces of red (paint?) in the treads.(see close-up). Originally there was more on the tire which I was able to remove with soap and water and a nylon brush. Ideally the remaining traces could be removed by soaking in some kind of solvent but I wasn't sure what could be used that would be safe for the rubber tire.