That's because purple paint denotes private property in these areas, which means you are trespassing and could open yourself up to criminal prosecution.
What's more, in a country where citizens have a constitutional right to own guns, disregarding these markings could put your life in serious danger.
| Those violent Americans are ever so quaint, my dear, with their odd ideas about private property. And of course, the guns they use to enforce them. |
However, it's important to note that in North Carolina, Virginia and West Virginia, purple paint is not for dissuading criminal trespassers. It's solely used to notify people that they are not allowed to hunt or fish in the marked area.