If you're out hiking or otherwise wandering around and you see fence posts and trees and such marked with the color purple, stop! You're about to go too far...

Marking posts, fences, trees, etc with purple constitutes a legal, "No Trespassing" sign in Texas. Replacing and maintaining regular signs is difficult and expensive. To make things easier on landowners, the "purple paint law" ,,, officially known as Texas Penal Code 30.05. ... went into effect in 1997.

The markings must be:

vertical lines of not less than eight inches in length and not less than one inch in width; placed so that the bottom of the mark is not less than three feet from the ground or more than five feet from the ground; and placed at locations that are readily visible to any person approaching the property and no more than: 100 feet apart on forest land or 1,000 feet apart on land other than forest land. - tpwd.texas.gov

Trespassing is a misdemeanor in Texas. Class B for trespassing and Class A for doing so while armed!