It's stated in our Avatar/Signature info that signature image width should be no more than 450px. This size limitation is out of consideration for those with smaller monitor resolutions -- to eliminate the need to scroll horizontally to read posts -- and slower connections -- to reduce image loading time. Also, it's to keep the focus on the content of the posts themselves, since the main purpose of this board is discussion.
Please keep this size limit in mind when you create or have created a signature image. We are willing to allow a little "overage." But if your current banner is very much wider than 450px (i.e. over 500), we ask that you resize it or have it resized.