I think the EXPERTS on Colorado Narrow Gauge railroading history will be more inclined to tell you that it was a handrail. First thing to understand, is that the purpose of the “Drovers’ Caboose” was to transport, the rear end train crew, but also to transport the “Drovers” who looked after the cattle/sheep being transported. They often had to walk the tops of the cars in motion, in order to make sure the live stock were not getting trampled, or injured. They needed to safely get along the “Caboose” roof, thus the handrail was needed.
Also the models with the handrails are the LGB and Piko models of rather old NG equipment, back when radios were not available, or invented yet The Stock cars/Cattle cars in service those days had small doors on their ends, so that a drover could crawl into the cars or at least look into the car from above, to see how the “Animules” were fairing…
Seeing as though the Passenger style Combine was being used as a Caboose, the train crew also had to walk the roofs, in order to work the brake wheels on each car…there were few cars, if any, in the early days that had air brakes…they had to be hand applied. The roof of that particular car made it hard for getting on to the roofs of the caboose, and stock cars.
The NG experts can agree or disagree with this speculation, and I will probably be shot down by some people in any case…
FJM