Közben feltettem a kérdést a jahún, íme a - CP-re vonatkozó válasz, de előbb a link, amivel illusztráltam a kérdést:

http://www.railpictures.net/viewphoto.php?id=180665&nseq=33


Szóval a válasz:

At the top corners of the caboose you will see that there are pairs of lights,
one each with a red or green lens. These are used in place of the marker lamps.
Instead of turning the lamp itself, just switch on the correct marker colour.
Only the indication to the rear is important.

Down low there appears to be another pair of lights, or rather, just the shells.
The lights would allow the crew in the caboose to inspect the track behind the
train. If a freight car had a wheelset derail, the train might stay together
for miles but the track behind the train would show evidence of the wheels
tearing up the ties. Once cabooses were no longer required, those few remaining
became "riding platforms", used only for reverse moves by industrial switchers.
The lights might be useful when backing over a road crossing after dark but
otherwise redundant.