These were the readouts for the hotbox detectors, with the instructions for the readouts listed in the timetable special instructions of the era.

If I remember right, there were also three lights about the numeric readout - which indicated if the defect was on the right, left or both sides. I know the detector indicated which axle the defect was found, but I don't remember off the top of my head what the default, error or multiple hotbox alarm displays were. Once the cabooses started being pulled off, there wasn't anybody to read them and they were changed to talkers.

Soo Line had (still does?) an interesting rule. Train crews were required to repeat the info back to a detector. It was a game to see how fast you could repeat it back.