I found a tally light project online here:
I designed my own circuits and 3D housing in Fusion 360.
The tally lights are built for OBS (Open Broadcast Software). They light up one of three LEDs. If the camera is “live” they are green, if they are “cued” they are blue and if they are “off” they are red. It’s really handy when you have many cameras all hooked up and automated views and such.