Good Neighbors?

 I live on a great street with good friends and friendly neighbors. With barely an exception Robert Frost was wrong, good fences are not needed for good neighbors. I don't think it is hard to be a good neighbor, be courteous and friendly and mind your own business. Say good morning when you pass a neighbor and everything else will fall into place. Everything was going great until last week when a neighbor posted the sign below. His property is all of 40' by 50'. Is it personal?