Stan Lee is the god father of comics, no arguing that, but he was such a signature whore, you can find his signatures on DC books he had nothing to do with, and I'm good with people paying stupid money for something you can easily find 24/7 in almost every comic shop or online seller.
Michael Turner was one of the hottest artists while he was alive, nothing hardcore about knowing who he was, since he did variant covers for both marvel, and DC, and had one of the hottest independent comic books when he left main stream comics. Long term, you will see value in the scarcity of signatures, due to his early passing.