There is really no black and white about the photography rule, but
my advise is ONLY take when there is no MRT Staff or MRT Police. As
long as you don't get caught is ok, but thats your own rule to
safeguard yourself.
But, take a look at it this way. You are taking photo at a
place where the staffs are in-charge, so you have to follow what
they say. Metaphorically speaking, if you go to people house, you'd
listen to your friend about where to go, what to do etc.. Same goes
to the station.. You are their place, you play by their rules.
Nontheless, please ask the Station Manager on duty, BEFORE,
doing any photo-taking at the stations, just to be on the safe
side.
But as I stated on top, either they do it all the way that hurt
your pride (The train fan's pride or confidence etc), that says a
big NO, and that IS their safe side, or they allow you (The train
fan's request) BUT, they are risking themselves either. This makes
you feel good, not only on request granted side, but you think that
you have ask already, feel no guilty or "I can answer to my heart
already" (问心无愧), but the back other side of the story that the
station manager will say is another question, which is something
that many people do not understand, resulted in earlier flamewar.
Today for my BVE development got some subsential progress, so I
will reply in a happy mood.