I find that Tibs...I mean SMRT buses staff do not mind me taking
photos. I took a photo IN FRONT OF THEIR OFFICE at Choa Chu Kang
Int. They did not mind at all 
But the bigger problem is placing the bus service guides at the
racks. Frankly speaking, we really do look suspicious when hiding
the guides
.
btw,I think these Transit Security are in plain clothing. I walked
around CCK and i didn't see any uniformed guards