Would you use a computer for this application?
This blog post covers ten bad uses of Windows. One of them mentions a great use:
only thing those monitors ever display is a big green arrow pointing down
Matt then goes on to note that this and another application would be :
prime candidates for a secure, robust Linux
Quite frankly this sounds like a prime candidate for a piece of paper. Or maybe plastic with a light behind it. Or maybe just getting rid of the sign and letting people use some common sense. Meanwhile here's a picture of a VLC error from our Prague holiday.