How can you tell if a MoFi disk is genuine?

Recently, I saw a copy of one of the more rare MoFi disks bought on eBay. It was good, very good, but definitly a copy. How can one tell if it is original? Is there any special markings or code on the inner circle that could shed some light on the authenticity of it?
I've often wondered the same thing, particularly with the CDs. Have you seen what the Wall and U2 Joshu Tree MoFi CDs go for? You wouldn't have to auction off very many to make quite a lot--and I've often wondered if someone has done just that.
I have almost every one including some wrapped and never used, but the open ones, I would gladly check the CD or LP to tell you what markings are on mine-They are originals bought way back when copying was not a viable option.
Not only is the disc gold but it is embossed with a black label that usually reads "Original Master Recording", has the album name and group name on it and will also have the record label of the company who released it on the label too.