Signature

Okay so I made my own signature and I have no idea how to get it in my 'signature' space. I mean when I finished the signature I got different options how I wanted the signature in code format etc.
Widget Code
Forum Code
Alt Forum Code
HTML Code
Forum Thumbnail
Alt Forum Thumbnail
HTML Thumbnail

But the problem is that none of this work since there always showing up some error like 'No URL allowed' or 'No IMG allowed' and that kind of stuff. Could someone please give me a short tutorial what I should do now after I've uploaded my image. Thank you.