I think a few people get the idea that, not being in a car, the cyclist is more vulnerable, a target for being bullied by a sign. For some, cycling is seen as not being in conformity with the rules of society, so a lower level of tolerance will be accorded. Anymore, generally, it seems that people are bothered by the slightest of things. Nothing like some real problems to put it all in perspective. Had a similar situation nearby. The residential to my north put up signs saying one could not fish, unless they lived in the two listed subdivisions, in the little pond nearby. I explained the basics of riparian ownership and public access from the adjoining trail when I was challenged about this. They decided to give up at about the word riparian.