I will take a look at my signatures on Saturday. I have several of Gretzky and I have gotten Coffey and Hull in person many times. The one thing about Brett Hull is that he signs using both hands. I have seen him sign two items at the same time, one with each hand. I have them on helmets, pucks, and photo's.
I will say this. Gretzky had a different signature in his early days, but changed to his more common style well before 1994, especially when he signed his contract with Upper Deck. My Coffey and Hull signatures on the helmets were from the mid 1990's, right around the same timeframe you are saying this photo was signed. Hull has some similarities and because he used either hand to sign, it could be good, but the Coffy is completely different.
I did just take a look and there are a few similarities. His matches mine a little closer though. Coffey is a little odd and not the nicest guy. I could see his signature being sloppy at times. Have you seen any others without his #77 added. Same this with Hull's signature without his number.