From Jim Starlin's Facebook page (where a friendly chap named John O'Connor linked this thread to Mr. Starlin's wall):

Jim Starlin: I signed the books on the tip-in page. I'm not sure about the numbering. Thought Image was going to handle that. I'll check on it with Image. (Yesterday at 4:00am)

So, that is indeed an original signature, but it's possible Image didn't take care of the numbering or did a very good job of hiding them. More to come...