A backlit sign we use during recording at Prusa Research :)
Article about it here:
The default backplate says "Recording - Quiet please", but I've also included an empty front plate, so you can easily modify it to say whatever you want.
I've used Prusament Galaxy Black for the body and the black part of the front plate.
If you want to have the same dual-color look, add color change at 0.8mm for the front plate.