http://blog.sfgate.com/bicycle/2016/03/22/road-thieves-of-th...
[0]: https://www.theguardian.com/us-news/2015/oct/02/california-w...
https://www.law.cornell.edu/uscode/text/18/641
Edit: I'm happy to hang out in an old pickup truck with a coffee and a shotgun and wait for someone to steal the signs. Just point me in the right direction and give me a number to call with the forestry service, national parks, or the bureau of land management when someone snags a sign.
I once called the Bureau of Land Management about repairing a dirt roads they liked to use that crossed private land. They made it crystal clear that it was an "abandoned mining trail" and not actually a road or easement, which in their mind relieved them of any obligation.
If you used it to access your land, you could start maintaining it.
I reality the ranchers(in reality they are usually rich sport ranchers that live in a city and recently bought the property) don't even need the closed gate in most cases. If you are in the middle of nowhere going down a dirt road and you come up to a fence that crosses the road with a cattle guard and on both sides of the road it say no trespassing, what do you do?
Closed gate with no lock, can't pass.
Closed gate with locked lock, can't pass.
Closed gate with unlocked lock, can pass.
Usually a cattle guard means no gate at all.