Authenticating autographed items: Madden
 

My mom has more crap, errr stuff for me to eBay. She has this football, new in box (Wilson) which has the usual brownish leather sections, except one panel is white leather and is signed, evidently, by John Madden. The one of the other panels also has ALL-MADDEN TEAM surrounding an old fashioned leather helmet design.
How can I verify it's an authentic signature vs autopen?

Gilly