Just for the sake of safety and to avoid being hassled by any local cops or DOT, I have been stopping at any and all RR crossing, regardless of how derelict they appear.
At any rate, in this particular part of the city, there are miles and miles upon more miles of railroad tracks that don't go anywhere, switch tracks that stop at a building (i.e. the land was previously owned by a railroad, sold to a private party, and the track removed up to the property line), signs for RR crossings where there are no tracks, tracks that are rarely used but not marked at all, etc.
It's a very screwy situation all the way around as far as being able to tell by looking whether or not a track is active. To give another example, about 3/4 mile away, there are crossing arms and signs at a railroad crossing - however, the rail stops approximately 30 yards onto property owned by General Mills (the cereal manufacturer) and ends in a big pile of weeds and debris. In the opposite direction, this particular spur connects back to a mainline that is currently in use by a commuter train.
Logic would dictate that any train that takes that spur would derail once it entered the General Mills property, so there is obviously not going to be a train using that crossing. At the same time, it is marked and does have crossing arms.....so.....
Stuff like that is what prompted me to ask my original question.