NEKBE sells enough original stuff and has been collecting for long enough to know the difference. No doubt in my mind that this is intentional and he will ignore your e-mail.
I reveived an email from the seller--his words, "i bought the sign from a respected Shell collection in S.Il,i think you are wrong".Looking at his feedback i think he is a shyster!
first...."I purchased it from a well respected Shell collection from southern IL....he guaranteed it real"
second..."I called the gentleman who originally had this sign and he said that it was indeed real.....why do you think that it isn't? I know there are reproductions out there but not exactly like this one."