I am part of a endurance racing team and one of the problems we have with the drivers is communication. A pit board is great but doesn't work at night, we have radios but have had them break several times.
So this is what I made :-
Carbon tray
Back lit with LED's.
Then cut out and an opache perspex front.
Black vinyl letters on clear backing are then used as the numbers.
Why Carbon Fiber ? because it's cool and I had some. The composite section is very light but all the LED strips make it heavy but still okay to use and wave from the pit wall.