Oh ok, Ed. That I didn't get, but thank you for clearing that part up.
My experience was this: I visited the T last December (see the Boston PCC article on this site)... I got a photo permit and wore it around my neck at all times. Was only approached twice by friendly employees. Keeping the photo permit in plain sight helps avoid a lot of confrontation with employees, and actually makes them feel a little more at ease when they see you pointing a camera in their direction...
-otto-