I was once told off by a overzealous caretaker outside a Hindu temple not to photograph the temple whilst at a public area. I just gave a straight face and then continued because I know what I could do and what I couldn't because I had ever been inside a Hindu temple shooting portraits of priests.
Seriously, I think there's no need to be so concerned about where you can't shoot. There are plenty of place that you can shoot apart from the obvious high security areas. In case of doubt, just shoot and then decide what to do next. If confronted, just act blur, apologise, smile and walk away. Alternatively, if you're in a foul mood, then just challenge and question the authority.
But if it is not Singapore, then you have to be really careful...what's logical here may not be elsewhere.