I don't like the shape. Too square.
Also, the sigs look like they've been subject to layer upon layer of Photoshop/GIMP brush, which they almost certainly have been.
All of these are subject to very similar design - that is, there's a flat, obvious, ugly horizontal line going across the middle of all of them.
It's almost like you made the base sig, opened four instances of it, copied a different render onto each one, and then applied a different selection of filters to each one. And they're all borderless.
I'm tempted to say that the fourth is the best - only because the background is so bright that I can't see that horizontal line well, nor can I see the edge of the picture.