Oh, lol. Thought you were using Ps by now; my bad D: Anyway, I don't know if Gimp has a pencil tool, but if so, you can run a black 1px line around the sig to make a border. Simple but effective:). (I tend to take the easy way out and use blending effects to do the same thing in Photoshop, but w/e:P.)
THEY TOLD ME I COULD BE ANYTHING SO I BECAME A SIGNATURE PLS HLP