Granite and concrete blocks are installed as part of Operational Projects as hardening in order to provide safety for pedestrians. Many granite blocks have been repurposed from bridge rehabilitation projects across the City. These blocks are a sustainable solution that integrates seamlessly into New York City's urban environment. NYC DOT also purchases new blocks when needed.
A few years ago they put some rocks in low visibility corners in my neighbourhood after a few close calls with kids. Every once in a while someone still tries to cut the corner and hits the rocks. Often enough that the rocks need to be moved back at least once a year.
Now, in the US I expect the rocks will be protests as soon as the first idiot backs into one of the rocks.