I put a screen saver on a friend's computer:

C DRIVE FAILURE

which had him going, for a few seconds.

Christopher A. Young
Learn more about Jesus
www.lds.org
The good one (not completely my idea) was based on an analog noise level
sensor that detected people approaching and flashed REPENT! THE END IS
NEAR!


You could have alternated that with things like 'Duck and cover!'
'Head for the hills!' 'Judgment day is nigh, sinner!' or even something
completely silly like 'Eat at Joe's!'