Some fighters charge for their autographs. Other fighters won’t give them at all because people turn around and sell them on Ebay.
Then there are others who are very nice, maybe too nice, and sign an autograph for absolutely anyone.
For instance, here we have Matt Hughes holding up a T-Shirt he signed for the White Boy Society, a white supremacist group reportedly using this image on their website to help sell their shirts.
Bloody Elbow has the whole story including a statement form Hughes’ webmaster.