Generally, those markers are placed by the person who did the previous survey. They’re not really official designations of anything. However, if you look around, you will find things called survey monuments. Sometimes they’re embedded in the sidewalk, or the middle of the road. Out in the boonies sometimes there’s a little concrete pedestal that has the marker on it. Anytime you look at a recorded deed you will see a legal description of the land and generally that description will start from one of those monuments.