Just to throw a different light on it....
I was stationed over at RAF Lakenheath in the 02-03 timeframe. There were people who sat almost religiously off the ends of the runway, on the side of the road, and took pictures, wrote down tail numbers, takeoff times, loadouts, etc of all the aircraft that we flew, every day. I don't recall the base cops ever trying to stop them. If it's acceptable to us to allow photography of our forward based assets, I don't see why we should be paranoid about a trainyard in Mississippi.
When it comes right down to it, you can't stop people from looking at stuff that is in plain sight. If you don't want something photographed, don't put it out where anyone can see it.