For the most part they're pretty friendly or just leave you alone entirely. It's only that area that I've noticed that they get a bit strange.
It also depends on the level of gear you have. If you have a pretty big camera and lens, you can quite easily get spotted out; but you can always just give them the realisation that each and every person that walks by holds a smartphone with a microphone and camera. They're forever walking by the same location taking pictures, recording voice messages, or video calling someone. Your presence is no different, yet they don't stop the others.
Weirdly, you'd think the many companies that operate in such buildings would at least choose the buildings that aren't skyscrapers and made of glass if they really didn't want people to know what's taking place within. :^)
The building where we did the look up shots apparently would usually have security guards. We started off being quite discreet, but it was the 2nd of Jan and it was a Sunday - I think everyone was on holiday. After a while it was clear that no one was going to bother us. I think it was lucky timing. :)