"Public Transport Authorities" means SBST, SMRT, LTA &
TransitLink, the companies of the public transport system. But for
PTC, it is for public transport organisation that controls the
public transport system.
"Request Permission" means that you must seek written permission
before taking photographs of the bus interchanges. Do not take
photos without prior permission from the public transport
authorities (SBST, SMRT, LTA. etc.)
Thank you. 
It is to ensure the safety and security of our public transport
system. The Transit Security are now guarding the MRT & the bus
interchanges for any suspicious characters. If you are taking
pictures of buses, my advisory, please seek permission first
because as you had mentioned on this post, this is one of the
common targets of terrorism.
