How about your company's name in the background of the login screen? Or your company's logo? It will surely work with xbanner which is designed for the use with e.g. XDM login screens.
Many example configurations may be found in /usr/X11R6/lib/X11/xbanner and its subdirectories.
Documentation lies in /usr/doc/packages/xbanner, in the subdir html you find a HTML version of the documents.