Download the .gif that you would like to use as your signature.
Upload it to photobucket, or whatever site you'd like to use.
Get the [/IMG] code, and paste it in your signature.
That should do it. Got any more questions pm me.
Okay, I got this off tumblr, I copied the original photo link, when to my sig, and there's a picture upload tab on there, insert it and your done.
Message me your skype and I'll help you, if you would like.