Ah I see, edit your signature then when you do click the little picture of the tree thing and then paste the url of the picture you want to add. You can get the url by right clicking on a picture and clicking copy picture url. It'll only let you do this is you have enough posts to get lost of characters in your signature - otherwise you might have to download the pics you want - paste them into one picture and re-upload it to something like photobucket and use the url of that so that you don't need as many characters.