I know that feeling. My new tenant live above love to throw unfinished food thru the balcony and eventually some will land in my balcony. Those sand nikka really think that the country belong to him. KNN!
Already lodge complain to the management. If no step taken, I will left some leaflet like you did, and if those sand nikka still behaving like an arsehole, I will just leave some rotten egg on his door.