These are a few I heard about who are recommended. I talked to the one here in Canada for my David Prowse ones they come recommended as well as both helmets would be about $100 Canadian to get autenticated. The other are all in the States I believe. Hopefully this will help you out, I unfortunitly dont have the skills to know if a signature is ligit or not I can only go by the ones I have in my collection for Comparison. I do however have Billy dee Williams which I know is real as a friend got it for me at the Seattle Comicon and he charges $40, Carrie Charges $60, if you want a signature from them, Those is Comicon Prices which are good figures to go with. I am not sure about Marks though.