Read "Message Board Tricks" at the bottom of the page.. The "formula" no longer included img src. Strictly a bracket ([)img... if its an image, url... if it's a link, then a closing bracket (] ).. then copy the entire address..then at the end bracket ([ ), then /.... then img, again.. then a closing bracket ( ]).
And all of this with no spaces between the brackets and the address you're trying to post.
I don't think Donna would object all if you use gifs in her gallery.
And that's also the answer for you as to how to post a gif someone sent you. You put in a photo gallery first. Then it's on the net, and has a url.
And .. YES you can post more than one gif in your signature.