You are taking "locals" a bit too literally. It is just a social convention and these are small communities, it is generally understood that unless the property owner has socialized something different, those signs are for mining companies, yahoos from the city, etc. A lot of times if you are not from the area, you can often ask one of the local people the purpose of a sign in some area based on what you want to do. They'll often tell you that you can ignore it as long as you are just passing through. The signs are there to discourage people. In fact, they'll appreciate that you bothered to ask.
But again, if you talk to one of the locals they will tell you that. I always made a point of doing that, most people don't.
Anyone with a to mind to could easily drive into an active mining area on BLM land
I imagine 99% of people just want to pass through carefully rather than dump trash or graffiti anything.
More often than not, it wasn't that people were trying to behave badly, they were just careless and exercised poor judgement. A recurring annoyance was someone in the Bay Area buying an SUV and deciding to take it off-roading deep into the wilderness with no prior experience and being completely unprepared. In addition to frequently damaging their vehicle beyond drivability or getting it hopelessly stuck far out of mobile phone range, they would tear up the roads and land joyriding, leave gates open, run into the cattle that live in the wilderness, etc. I probably personally rescued people a dozen times who had no business being out there in those vehicles (an SUV off the new car lot is not equipped for that environment), with that lack of preparation, with that little experience.
Not malicious most times, just ignorant and engaging in poor behavior without understanding that they shouldn't be doing those things.
Maybe a well-publicised term for a private easement that people recognise is treated in a particular way? I like that in the States, National Park means something, BLM means something, etc. Our designations in Australia don't seem as clear. We have Crown land, but I have no idea where to find out about it.
Private easement guides would be: You are a guest here on private land. Don't stray from the road, leave gates as you found them, livestock has right of way, no camping, etc.
Surely there's a balance in making reasonable land access available to people.
Really this is called "sharing" and it's sad that it's causing so many problems.