I think it might help to know there is an interesting quirk in US trademark law... If an entity doesn't use and protect its trademarks, it loses its trademarks. As was mentioned, some entities got a bit carried away with it, and the lost the publicity battle - not to mention the Court battle.
This is why there are "heritage" units, if the railroad doesn't use its trademarks, it loses them...
Sooo... If you go to the railroad, hat in hand, and say "sirs, may I please use your trademarked logos for this purpose..." and they give you written permission, all is good. They've "protected" their trademark, under the law, and you have their kind permission to go ahead and use it.
One of the things that did come up in the simulator community, is certain entities didn't want their logos used in so-called "crash videos" on YouTube. I personally don't think that's the least bit unreasonable. Ever notice in a Hollywood crash scene logos of vehicles, etc, are obscured or given false logos?
None of it is unreasonable, unless you're referring to the law itself. Of course, it also protects others, such as the owners of #5, from having someone "trademark" the RGS and Galloping Goose logos and then charging them to use it.
Another interesting quirk, you cannot trademark a word. Which is why United Parcel Service became simply UPS and Federal Express became FEDEX.
And, incidentally, why Burlington Northern - Santa Fe became BNSF.
And, contrary to popular belief, you cannot copyright a font. It's not original, just another way to write/print the alphabet. Hence, Rio Grande speed lettering as a whole can be a trademarked logo (owned by its successor company, the Union Pacific) but the actual lettering style cannot.
Robert
