Aren't yards already fairly well-protected? And that's where most engines are. I feel that if the current vandalism isn't really much of a problem, there's no need to have officers sitting at every single siding where an engine happens to be -- which is probably too much anyway.The whole just shows the lack of security in the railroad business. Trains are often sitting around for hours in an unsecured location. If a high value intermodal train is stopped somewhere you would think a railroad police car could be sent to the scene. If might be enough to discourage any problems. At least if a raid takes place the railroad police officer could notify local police.
UP seems particularly lacking in security in the L.A. area. Have you ever seen photos of locomotives used on locals in L.A.? They are covered in graffiti! You would think the railroad would care about people painting over their locomotives! It's a wonder the locomotives aren't stripped for parts. Why would UP leave locomotives unguarded overnight?
As far as blaming the homeless for this, I doubt if homeless people would be organized enough for such an activity. It's more likely criminal gangs like the ones that invade high-price stores.