I'd say that this looks legit. There are many signatures instead of just one or two, and it would be hard for a scammer to pull it off (not referring to the OP, since he got this from someone else).
But, of course, having some sort of original documentation to authenticate the signatures always helps. Including but not limited to: sales receipts, contest letters, unique memorabilia to accompany the signatures, etc.
In any case, that's a pretty incredible find, and it looks very cool!