The holes, their locations, the lack of grommets, the finish, the back of the sign
at 3 and 9 o-clock position on the originals that wide blue stripe is not there
Unfortunately this info helps the crook more than the victim.
Without fueling another thread on reproductions and their harm to our collecting community, we gotta all know the day will come when perfect reproductions will be made that'll be virtually indistinguishable from an original.
I think COA services for advertising collectables will be popping up real soon. I say within a decade it will be the norm to buy or sell signs or globes with one. Exactly as it is with sports memorabilia and autographs. Not saying that's good or bad, just my guess it will happen.