I will take a stab at this. Since traditional ad glass is flat and, well, made of glass, and these are made of plastic and three dimensional, I am wondering if there wasn't some application like the pic I have attached. Those acrylic signs were often backlit. I wonder if these signs were somehow incorporated into that type of use? This is pure speculation.

Texaco Lighting.png
Alex
Looking for Texaco and Power Gasoline items