#1:This seller sells/advertises fakes all day long....
#2: An "original" porcelain sign will be porcelain on both the front and the back....
#3: I'm not an expert on Firestone Signage, but I don't remember seeing such a size sign before....
I'm sure those that Firestone Collectors on the site, will be able to help you more and will possibly send you a PM if you want more information....