Baseballfann, I don't think he meant it in a negative way. What he was trying to say that they could be better with the right software. I've noticed your sigs and I think you have loads of talent, but you need to maybe get an upgraded program or work on cutting your images out.
Trust me, I'm impressed with most of your stuff.
I agree with crum and gjg, just work on cutting out your images, it will make things look a lot smoother. You should also check out http://www.goodtutorials.com
(its written for photoshop, but as long as you get the basic jist of the tutorial, you can probably get a similar result for the gimp), or another site like that, and they might help give you some ideas for backgrounds and effects you could use that would make your sigs look more "professional". I also agree with crum in that the guys who do graphics around here don't do it for the logo, but because we enjoy it