I’ve read somewhere that threads in all emergency light bulbs in subways are inverted. That way they would not fit into a normal socket, and make it harder for would be thieves to steal them. Regular bulbs, like the one on the picture supposedly have normal thread because they are always on and thus hard to steal because of their temperature. This bulb is not store bought – note the NYCTA logo on the bulb.
I didn’t know the difference between NYCTA and MTA. Pretty interesting.