you should bring up to the building that this is happening and maybe see if the building can chip in with a deterrent.
One of Hotels my company manages in Edmonton used to have a problem with teen crime and drug addicts, so what they did was add a noise deterrent.
Its a mosquito buzzing noise that deters people from loitering around.
I dont know which the hotel is using, but I searched google and first thing the came up was this:
Mosquito Device Anti Loitering
It has worked dramatically for the hotel, so I hope this might help you as well.