Not that many years ago most of the property in my rural mountain neighborhood was unimproved, and consisted of parcels from 2 - 49 acres. However, a subsequent building boom quickly raised real estate values and inspired many of these long-time property owners to sell. Most of these sellers purchased their property years ago as an investment or perhaps to one day retire and build a home in the mountains.
The new breed of land buyers is difficult to categorize as a group, except that they appear to have more money, and they are definitely paranoid. Perhaps they are all city folks who feel the need to lock up anything they own when they are not able to watch over it. You can't lock up unimproved land, but they try. A fence is the most obvious choice. A locked gate is the next best thing, and this new breed prefers both. They have no livestock to keep from wandering away, so the fence has no practical purpose other than to say to passers by: "This is mine and you can't come in" - similar to dogs who pee in each corner of their territory as a way of claiming it. But even more than a new fence and/or a new gate, the real evidence that a property has new owners is the brand new "No Trespassing" signs which appear. They come in various official-looking forms. Some say "Posted " Others refer to the county sheriff and the possibility of prosecution for stepping on the unimproved land. Never mind the fact that the new owners don't live there and only come visit their unimproved land once or twice a year.
The owners who most amuse me are the ones who have no-trespassing signs on locked gates. It would seem that the statement made by a locked gate was clear and sufficient by itself. The addition of a no trespassing sign seems redundant, overly possessive, unfriendly and paranoid. "No Trespassing" signs do not deter criminals. Neither do they deter wild life. The only deterrence is to people like myself who would do no harm and have no bad intentions.
I purchased an additional 8 acres of land that contains no signs, but I decided to put one there. I have no gate or fence, so I had to put it on a tree. It says "TRESSPASSERS WELCOME Come see the view!" I don't think the signs makes any difference in the amount of traffic across my property, but it is more pleasant and neighborly. Besides, I don't really care if people do a little exploring on my land. The view is very nice. Perhaps Robert Frost was correct when he said "Good fences make good neighbors," but "No Trespassing" signs just annoy people and make them nervous while they are exploring your property.
Post Script: I've had several responses to the above, and they were mostly negative. Our society has become so litigious that evidently many people really are paranoid about being sued. But if someone falls and busts their ass on a piece of unimproved property, I don't think that there is a court in the country that would blame the property owner, whether it be a private citizen, the BLM or the Forest Service. And if I'm wrong about this, then our legal system really sucks more than I thought. With that said, I'm not adverse to putting up "No Hunting" signs. I'm all for freedom to roam, but not freedom to kill things. Perhaps a "Tresspassers Welcome! Hunters Not Welcome!" sign is the answer. Sorry hunters. If you want to kill things, go to Afghanistan or Iraq.