Have noticed Mark Gasnier has started to change his auto noticed just before he left for France to play Union 2 or so years ago, then occassionally he would revert to his "normal" auto now back to his crappy auto, i have a theory if he thinks your a seller he may do this crappy auto, is this his way of some sort of payback...
Note: I don't consider myself a seller, more of a collector, I have had heaps of item signed by Gasnier over the last 10 years, 95% have been for my PC have sold 1 jersey, couple of caps..
yeah I had a look at the 2001 FF signed By Gasnier which is similar to the one signed on the jersey. I had spoken to some raiders players inregard to this and they advised they do it mainly to sellers as they don't want people to profit from there autograph unless licenesed
Its quite common for players to have 2 signatures, there normal 'better' one, and then a shorter one. Usually do there shorter one if they are in a hurry or if its on a card or there longer one on a jersey.
James Hird and Andrew Bogut are two I can think of off the top of my head that do this.