Pretty sure there are always snipers on the roof.
You can't see the really good ones. :)
I'm pretty sure they are there 24x7 following changes after 9/11.
I've been on the roof.
I know of the changes put in place after 9/11.
Just because you can't see them doesn't mean the policy has changed.
Or more specifically, when you do observe them from a webcam that it means something is going on out of the ordinary.
That's all.