My understanding was that staff at the publisher signed the copies that weren't done by "Beryl Evans" at SD ComicCon.
Robin is one of the nicest people I know and we've become personal friends as well as business associates. Steve has joked that Robin knows more about The Dark Tower than he does!
So, some random person signed my book, cool. lol. They do have a very nice fake signature tho.
And I can totally believe that Robin might at this point know more than Stephen the way she way just going on and on without any reference to points in the book, places and characters. But I mean it is her job so, guess its expected. She told a few funny stories about how she had to remind Stephen that he killed a character off a while back when he was writing them in to a new part of the story, and how one time Stephen just randomly send an email asking her "Whats in Jake's Backpack?"
I can certainly see after only spending a few hours with Robin that her energy and pleasant demeanor can be contagious. It was a really smart choice to have her do the tour, if it was just some movie rep. it would of sucked. She was by far the best part of the whole thing.