Maybe this guy loves his lawn a little TOO much.
I agree with everyone that you absolutely MUST pick up after your dog. If on the rare occasion you are caught without a baggie, that means you have to pick up someone else's poop at another time, or your poop karma will be out of balance. You don't want a big pile of dog poop hanging over your head.
I see a variety of signs around my neighborhood, varying from "Please curb your dog" to missives similar to the OP. I do find myself irritated when I pass by a sign lecturing me to be a good neighbor!!!!!!! and to show some consideration!!!!!!!!, because the sign kind of defaces the property anyway.
Some people are more pragmatic and put some kind of decorative barrier around their garden. You can have a simple, low, wrought iron fence, and your problem is solved. Someone else I know puts bamboo sticks all around her flowers. Very pretty, and also sharp.