if it's for like promoting it on other sites/forums, go with something like this:

http://img.photobucket.com/albums/v234/SwissMiss33…..s/GTA4.gif

350×19, those seem to be a popular size for signature extensions. Hell, maybe I'll even make one . You can see other examples in this guys sig over at another forum, which I am a moderator of: http://www.gtawh.com/forums/index.php?showuser=8

Also oly1kenobi, welcome to the site! It's definitely picked up in the past week and we got lots of new faces. Would be nice to see you as a regular on here! As far as the store update, that's all dependent on when it actually becomes available, seeing as it's posted online, usually when it goes live, hence why it's not up yet :/. Should be soon though, usually up between 4 and 5PM MST

EDIT: looks like those sigs are called Userbars

EDIT #2: Here's a quick one I made: