Dark Angel, to use a banner in your signature you need a web space to host it, or ask someone to host it for you.
I'm sure Fortune can host it if you don't have the possibility to get a webspace, if you ask.
Then, you go to your control panel and edit your profile in the space you have to put your signature. Yuo just have to put a link to your banner using image tags:
[img*]URLofyourbanner[/img]
obviously, you have to change the "URLofyourbanner" thing with the real URL, and don't use the * inside the image tags. I had to put it to show you, but you don't have to put the * inside the []