Go click on your profile settings, then click on signature. You upload images into it, but if the image URL is too long, it won't work so use http://goo.gl to shorten the image URL.
I mean, I do it right but it cuts out half of it and says its been modified and read the rules and stuff
What you have to do is go to your profile thing on the homepage. Then, click on signature. Lastly, click the little picture icon and insert the URL to the photo/gif there. Hope this helped.
Shorten the url. Go to www.goo.gl to shorten your url then use the shortened url for the image. Hey on second thought, can you send me the image so I can try it myself? Just to see if it is possible or not. ;)