I know this is an old discussion, but for my deployment, I've written a small(ish) script which changes the logon wallpaper to a red background with this sort of layout:
Computer name: wsblah
Make/Model : blah
Serial number : blah
Operating System: blah
Do not attempt to use this computer
(custom message)
The script is called with a parameter $reason. If that exists, then it's a red background and the custom message. If it isn't then the background is blue, and the "do not attempt... " bit is our company name.
I can post the script somewhere, so long as nobody laughs too much at the decidedly dodgy coding!!
