Shane,
I think that's about right. Class lights would only be found on a locomotive (or maybe a self propelled vehicle like a RDC or MU coach). Their color (or absence) indicated the general class of train. In the rule book they were generally referred to as "signals". Never did understand why it was signals in one place, and "class lights" or "flags" in another. The old rule books were not exactly user friendly.
Markers are on the end of the "train" which could be anywhere from the rear of a light engine to the rear of a caboose, or maybe just a red light or red flag hung from a freight car coupler if there is no caboose on the end of the train.
There was as old cliche that a "train" was anything between a set signals and markers. Except some trains didn't have signals.
In the old days a lot of gray cells could be spent discussing unusual combinations and permutations. For example, where do the class lights go on a locomotive running tender first. I believe they still go on the smoke box front, but I don't really know for sure. And rules did vary from road to road. As mentioned above the DRGW used red and yellow in their markers, other roads used red and green. And if you go back far enough even the colors had different meanings over time.
Discussions like this are useful because there are fewer and fewer of us who remember how to run trains under trainorder and timetable.....mainly because it is totally useless information these days. But remains a fascinating historic industrial art form.
John