I can't see any reason to presume guilt - what we seem to unanimously agree is not a genuine signature perhaps draws undue focus on the disclaimer. In fact, very few people will or can certify signatures. Sure, if you handed the writer the copy of the book you might be well inclined to do so, but even when there's a consistent number on a copy, the number is in the correct color ink, position and hand, and a sig looks good, I'm not sure what it would take to actually certify that it is genuine or how many of us us would actually do it.