I made you like sprites, go me. Anyway, back on topic. The big orange thingy pulls my eyes away from the sprite, so maybe you could set that to overlay. Other than that it's a sig well done.
Move the spite to the middle, take out the orange blob, and make the bg black, and it's an OKAY tag. TUTORIALS ARE YOUR FRIEND. >_>
I took a tutorial.... http://www.gimptalk.com/forum/topic/Sprite-Tag-23969-1.html#184926 That one to be exact.
not bad you probably should have used a different color than yellow for the part on the left, and used a darker background though thats all i would do to it.
Remove the semi-border, BIG orange blob, and background. If you try to do a sprite-sig, it's better to use more of GIMP's filters over brushes. Also, change the background to pure black. The grunge brushes kind of ruins the effects around the sprite. Reduce the size of the whole signature so it's more proportionate to the sprite. Unfortunately, that's all I can think of right now.
Well, follow the tutorial fully. You aren't in the stage where you can go off on your own(well, alot.), IMO :/