All trains regardless of era or type are required to display "markers" that denote the end of the train.
The rules vary by railroad, how many mains there were, whether the train was moving or stopped, on a main or a siding, etc, etc., so if you want a really, really detailed answer consult a rule book for your railroad and era.
Having said that, the general rule, which is also consistant across railroads, train types and eras, is that the rear cars has to display a red marker to the rear. That marker can be a red flag, lanterns on the ends of the car, a red light or lights built into the car, a reflective red panel or an EOTD.
So if its a passenger train, it might have lamps on the sides of the car ends (much like a caboose) displaying red to the rear, or maybe just a red flag on the rear car.
The purpose of the marker is generally misunderstood. Its original intent was NOT like an automotive tail light or a stop warning. What it said was, "Tha that's, tha that's, tha that's all folks!". It told opposing trains that the entire train had arrived or was by a train or location. Until a train saw the marker go by it could not assume that an opposing train had arrived. The train may have had to double into the station, the train may have broken in two (very common back in the link and pin eras when the rules were originally written) so there may be a portion of the train still sitting on the main track. Untill that marker came by and told the train being met that the WHOLE train had arrived, the train being met couldn't leave the station.
By the way, the vast, vast, vast majority of passenger trains (maybe 1000:1) ran without observation cars. Its just people liked to photograph and model the high end trains with observation cars. There might be 200 commuter and short haul trains operate out of a major station for every one premium train with an observation. Regardless of whether the train had an observation or not or a caboose, the same marker rules applied.
Dave H.
