Well, if you're talking about the image, then this is what you do:
Put your mouse directly over the sprite, right click it, go all the way down to where it says "Properties" There you'll see a little box appear on your screen. One of the lists in it is labeled Adress(URL), highlight the url in here, then go to your profile. When you're changing your sig, put the url between these: [ i m g ] [/ i m g] without the gigantic spaces of cousre. And the image should appear.