A signature is simply text that is entered in the posting textarea before you begin typing in the contents of a node. The signature can be editted for each node if one so desired to do so. So when you submit a node with a signature, the script does not know where the signature begins. It could be made so that adding a signature in User Settings would automatically wrap that text in a <div> tag, but I vote against that.

Besides, what's the point behind wanting to hide who wrote a post? Wouldn't that just make us an anonymous community? What happens after I spend all my votes? I'm not allowed to view the authors of the posts I didn't vote on? While it may be true for some monks that knowing who the author is makes a difference on their vote, taking names away wouldn't help. There are times when I don't even look at the signature or the author's name and I know who wrote it. With time, you get to know the way certain people write :)

[ Signature removed to conceal my secret identity ;) ]