Answer: In Texas, as well as several other states (Illinois, Missouri, North Carolina, Florida, Arkansas), purple paint is a method of
prohibiting trespassing. Basically, the purple paint is one alternative to posting “No Trespassing” signs. The Texas Penal Code 30.05 provides that a person commits criminal trespass if he or she (1) enters or remains on the property of another; (2) without effective consent; and (3) the person had notice the entry was forbidden or received notice to depart but failed to do so.
In order to constitute the required “notice” that trespassing is prohibited, purple paint marks on posts or trees must meet the following criteria: (1) vertical lines of not less than 8 inches in length and not less than 1 inch in width; (2) placed so that the bottom of the mark is not less than 3 feet from the ground or more than 5 feet from the ground; and (3) placed at locations 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.
Thus, in summary, purple paint is used to indicate that the public is not permitted to trespass on private property and is one of five alternative options for giving the notice required so that trespassers may be held criminally liable.