There is a tendency in some inner cities in Britain for buildings to have ‘spiky bits’ on suitable ledges aimed at discouraging people from loitering. In Bath there are a number of such perfectly suitable ledges that people could use to sit on and rest but which discourage sitters with their spikes. I have nicknamed these Bath Crocus.
Video - Celluloid for thought
Some Wingless Angels - a movie by Spiky [youtube.com]
Bath Crocus - a lot of spiky bits