Okay, looks like his signature is going to be legitimate - Here's a bullet point directly from the 2k site:
* Exclusive Collectible Art Card Personally Autographed by Hulk Hogan: The Hulkster himself signed thousands of these cards specifically for the "HULKAMANIA" Edition of WWE 2K15. We sent him the Sharpies and have the photos to prove it!
Source: wwe.2k.com
Also read elsewhere that the run size may be ~25,000 and that seems about right with there being approximately 57,600 sq. inches available in a ring.