"Ikezu" is a Kyoto dialect word meaning "mean."
A mean stone..
In Kyoto, they can be found everywhere in residential areas with narrow streets.
Residents place stones on the boundaries of their private property to say, "Don't let your dog pee on my wall," "Don't park your bicycle on my property," or "Don't enter my property."
So, even if a passing car is damaged by the stone, it is the fault of the car that entered the private property.
This is to prevent any troublesome communication with the owner of the car.
Good idea, though not a very kind one, that suits the temperament of the people of Kyoto.