Signs like this one telling people not to leave their dog's feces all over the place are abundant in residential areas in Tokyo. There wouldn't be a need for these signs to be plastered everywhere if people weren't leaving poop behind when walking their dogs.
There's a back street near my home which I always take to go shopping for groceries as it leads to a wonderful shopping area not too far from my apartment. The street is often traveled by pedestrians, but not in great numbers, and particularly not at night. It's also very popular for people to walk their dogs along when they need to "go walkies". Though there are rules (possibly even laws) in Japan about picking up after your dog, people who take their dogs out to do their business on this street frequently do not clean up if no one is around. It's so bad that every single day when I walk down the street, it smells like dog crap and there are piles of it in various parts of the street (which is for pedestrians only, not an area for traffic). This is despite the fact that people who live in those areas are cleaning up the street in front of their homes everyday. That means there's a fresh layer of crap being left behind on a regular basis.
I won't miss seeing and smelling the results of people who willfully and blatantly ignore the rules or laws about cleaning up after their dogs simply because no one is there to see them do it.