You could do this a couple of ways. Outputs can be set to have different run state settings. One those is high when stopped so a light would turn on anytime the program is not playing (stopped, paused, protective stop, etc) and this would be automatic.
The other option is to let the PLC do this. You can access the robot run state via EIP or Profinet and then you could determine to only turn a light on when paused or when in protective stop, etc.
Do you guys know if there is a way to turn on an indicator light if the program is paused? I have the robot wired to a plc to control the light but since all of the built in assignments for the start,stop and play are only assignable to inputs(for buttons I am assuming) i am nt sure how to access the robots program state to enable an output when its paused.