My current job puts me between the right-of-way lines as a consultant and not a RR employee. There, I can see Dick's point. The RR employee-in-charge is MUCH more apt to react to the presence of a "foamer" in "tourist" or "geek" attire than if a guy shows up with a camera for a quick shot looking "at least halfway like he belongs there". I normally carry a camera on the job to record construction activity or to document contractor's work. I am generally able to fire off a few "train shots" with no problem--but much of my work happens in less-than-scenic locations.
I have a huge dilemma during my non-employment "RR photography trips". Yes, I do carry ALL of the safety gear--including an item that hasn't been mentioned that is a REQUIREMENT--a hardhat. I do know some railfans that carry them, but have yet to see any "unauthorized" person actually wear everything necessary. I also have my vehicle registered in a contractor's database and have a paper in the window. I am also overly aware of the right-of-way lines these days. As much as possible, I make the attempt to photograph from "legal" locations. On those increasingly rare "unauthorized access" instances, I either make it a "hit-and-run" shot, or one where I am not too obvious. I have found myself more often than not, wearing colors that don't attract attention. We have to remember that safety is the RR's #1 concern. Trespassers who are NOT railfans (or their surviving families) will generally sue the railroads after an accident, so the RR legal departments make the policy. Since 9/11, the FRA has imposed the unfunded mandate (typical of the over-reaching Government) of fines TO the railroads for "NOT securing the property". Remember, it's not always a passing RR employee who can call his S.A.'s over OR call the local police, it's a passing FRA inspector (in an unmarked vehicle) too. These guys then hit the RR in the pocketbook which makes them even more cranky.
The main thing to remember is to do NOTHING that raises attention. If you are in a LEGAL location, but one that might raise the concern of a nearby resident, etc. Put up a tripod (even if you don't use it) to let anybody know that you are a photographer who is waiting for something and not somebody "planning something".