In Illinois, Iowa, and Missouri, it has to be explicitly signed via actual signs, or purple paint (relatively recent laws allow this in rural areas). Alaska req

In Illinois, Iowa, and Missouri, it has to be explicitly signed via actual signs, or purple paint (relatively recent laws allow this in rural areas). Alaska requires signs. Indiana requires signs. Those are the states I am familiar with. I believe the states that do not require notice are in the minority, but I'm not sure how to prove that.