The tiny, tiny battles over dog poop and pee as well as even sidewalk inches are (an unwelcome) part of the dog-owning experience here in Gotham. Like most crazy New Yawk things, it does have two sides.
My own theory about people who lord it over a tiny corner or tree with their no-poop, no-pee signs and the like are that they are trying to exert control over this diminutive kingdom as so much else is out of their control. A few (and I respect them more) are plant/tree activists who consider the foliage every bit as alive as our animals.
People have said the wildest things to me when out with our various dogs, especially Nova as he's so interactive. My favorite was my first meeting with Bernie Goetz, the ex-subway vigilante turned squirrel rescue poop-bah. On a snowy day in Union Square, he scolded me for my dog's "frightening the squirrels", which was kind of funny cause my dog doesnt even chase them, but sits regarding them like a TV show.
You must understand the other side though - some dog owners are so flagrantly selfish and have such disastrous relationships with their dogs that its a wonder there arent more of these zealots.
I cant count the number of times Ive see people come into a park, let their dogs off leash to tromp all over flowers or new lawn, then leave poop everywhere. Ive seen people with dogs the size of cattle pretend they didnt see their dog poop. And then there are the ones who take their dogs offleash and proceed to ignore them, whether they be attacking another dog, jumping up to grab food out of a hapless bystanders mouth, etc.
It DOES take both of these things, self-appointed neighborhood dog wardens AND clueless, entitled or just plain irresponsible owners, to feed behavior like you experienced on your recent walk.
I know those kind of run-ins can be upsetting, and you tend to take them with you for a while. At those times I choose to remember how many committed, extraordinary dog owners there are in this city, and how many wonderful dog fans we meet every single day on our rounds.