Like I said, get the image url, like upload to imageshack or tinypic or something, if you tinypic, the [IMG] Tags come with it, so upload your image to Tinypic, If you don't know how to do this, go to Tinypic.com, Press "Choose File", find the image you want to upload, then press "Upload Now", then a captcha will come up, fill it in, then press "Upload Now" again.
Now your at a different page, find where it says:
IMG Code for Forums & Message Boards
Now copy that code, go back to e*pvp, and edit signature, then post that code in the box. Then save it, it's that easy~