If this was simple to do, that would be fantastic!! It seems to me that many owners do not live near the property, could live in another state, or be difficult to get a hold of.
I did this in San Diego County several years ago. After calling, leaving messages and emails to the local forest circus employee responsible for land status. He did finally answer the phone. I said "there is a forest service road going up to a huge plateau that is "mostly" private property, however there is considerable forest land as well." I said "this owner has installed razor Concertina wire and posted private property, violators will be prosecuted signs all over your gate that is on public forest service property. This property owners property is 150 yards beyond your fence." The forest circus employee said "Well the owner is doing that to keep people from trespassing on his land, because he doesn't want to post and fence his land, and besides he had trouble with trespassers decades ago." I said "REALLY??, you know you aren't supposed to allow that!" He said "Ahhhh....you are right." I said "you need to take that crap down." He said "Ahhhhhh, we don't have the resources, but you will not get prosecuted for trespassing, because it is public land." Then I hung up......
That ain't my problem. It's time and patience and they are in very short supply, lol. Cheers Bill