I will be honest, because honest criticism is the only way you get better.
Your 'sigs' are terrible. Badly cropped and warped images pasted onto a black background with poorly placed, mispelled text in colors that clash horribly with the black and seem determined to blind all viewers.
Yeah, you're pretty limited with Paint. So why don't you check out one of the many programs (a lot of which are free or have free trials) that are linked to in the resources thread?