I see a symptom that is caused by a state of mind. The frequency of such symptoms is measurable and has been increasing over the last 2 decades and not for me to identify the source without causing trouble.
However my query, which I would try to add clues to from passing observation, would be does the motivation of the temper of this sign come from farmer or landowner. If a person, who clearly dislikes people straying onto 'his private land', feels it necessary to be so blunt, then I would feel that I would not wish to buy the product of that farm.
There have been great advances in the product identity and public relations of the British Farmer to identify sources back to farm gate. Such visual examples would have far more value if they were tagged with location, to encourage identity of the occupier.