Dollars to donuts, this is an RR7 kind of deal
In this system, you have a relay back at the service panel or control cabinet. You then run 24V low-voltage power to each switch and motion sensor.
The most common, the RR7, is a latching relay. If you send control power to the relay for 1 second, it "throws the relay over" and it stays there until it's thrown the other way. Each bank of switches gets a 24V supply wire, and it returns an "on" wire and an "off" wire for each string of lights. Energizing "on" for a moment throws the relay "on"; "off" does the same.
The neat thing about RR7 is you can have any number of switches controlling a light, and wire it with thermostat wire. Also, you can have automated systems work very easily with it. Say you want to turn off the lights at 8 pm, because people always forget to turn them off, the timer just pulses the "off" wire for 1 second at 8 pm.
There are different systems
For instance one system has only one on/off wire, and energizing the wire for 1 second toggles the lights on vs. off. That works for humans, but a machine (eg. The timer) needs a feedback wire to tell machines if the lights are already on or off, otherwise if they're off, the timer will turn them on at 8:00. Anyway, that light may be this feedback wire.
These commercial systems are generally hard-wired old-school, because that is reliable and doesn't require a geek to troubleshoot balky software.