Ask yourself... how would a station use a 8"x18" tire advertising sign? if you cant visualize it, then stay away. try to think of the HISTORY of these items...
Having very little knowledge myself to authenticate an original sign, I asked myself the question you posed. The 1st answer that came to mind was that a station could use it on a column near a pump island. The problem is that I could visualize a sign of this size pretty much anywhere at a gas station, so I'm not sure how being able to visualize it helps to determine authenticity?
