On a lot of the trains I've been on in various parts of the world, those cars are usually the first car or last car ... and whether they are or not, they are usually marked with a little bicycle sign or something. I've never seen anyone attempt to take a bicycle through the aisles on any of the trains I've been on, nor have I attempted it myself.

I'll ask when I get the ticket if there is a specific car for the bicycle. If there is, they'll tell you either specifically which one ("Yes, the baggage/bicycle car is the first/last car"), or give you a general idea ("Yes, look for the car with the bicycle logo outside it ... it's usually near the back"). If there isn't a specific car, they'll usually look blankly at you and then slowly say something like, "No, just put it on wherever it fits."

You can sometimes get additional help/information from the conductors ... they will sometimes point to the right car when I'm dashing along side the train, or shout out that it's the last car or something.