What did you actually do to it? It looks like you added text and called it good. And I don't know how to do this in GIMP, but borders, around 2-5 pixels make sigs look phenomenally better.
http://podtacular.com/forums/viewtopic.php?t=14467 http://podtacular.com/forums/viewtopic.php?t=19865 A few tutorials for you.