I wanted to use an image as my forum signature, but everytime I try to update it, it says I can't because I already have one image. But I don't even have a forum signature.. I'm confused. Someone help me! :) That would be much appreciated.

Apparently this is a problem that's been going on for a while -_-. There's already a thread here. From what others have said, you can try putting the image in your forumtext.

In addition to what said, another user said you can get around the error by using the alignment code instead of the regular img code. It's kind of an annoying glitch, but at least there seem to be a couple ways around it. p: