Need to display security classification on monitor

I have a need to display a security classification on the display window for all users of a windows 2000 pro pc.

When any user logs into the PC, a small block of bold text OR a small image displaying CONFIDENTIAL should appear and stay on the screen regardless what application they are using.

How can I do this? thanks in advance for any help. This PC is part of a win2k domain if that matters.