You can insert up to three URLs (plain text links) OR three images, (or any combination thereof) - but the images have to be quite small, otherwise they will muck-up the display... But you will find it's best to stick to one or two URLs and only one image. Otherwise you will keep getting error messages when you try to create your signature.
Full Members can not insert HTML. Not even moderators are allowed to do that. It is just too dangerous for the security of the site. So that pretty well rules out banners - unless they are just plain images without any embedded links.
The other thing to realize is that your signature only shows up in your Forum posts. (These things are really just a hangover from the good old days when Forums-based websites were all the rage...)
To create your signature, you will not find it under Edit Profile... You need to go to your Account Settings.