I think the terminology is "box vent". They seem pretty common in photos of baggage cars and RPOs. There seem to be a lot of variations in terms of size and the shaping of metal- speculation on my part, but I would suspect that many were done in railroad shops rather than as a standard part. They also seem to be commonly retro-fit, that is, you see a builder photo of a car in, say, 1920 with just screens in some of the clerestory "windows" and by 1940 most of the clerestory windows are covered, there are more or less screens, and often 2 or even 3 styles of vents have been added.
If you have some handy, take a look at the MTL roofs for their diner and mail-baggage. (there may be more, I just happened to have those at hand).
