While taking a hike or walking through the countryside, you may see many different colors – the green of the trees, the pink of some flowers, the brown of the dirt, the gray of the rocks – but if you happen to come across a post that is purple, you should turn around and walk away.

Often, the posts are part of a fence and they have been colored purple not for decorative flair, but rather as a way for their owner to send a message to people who encounter them. That message: No trespassing.

You might think a “No Trespassing” sign would be more effective, but signs can fall or be taken, so many landowners instead paint their posts, and the law is on their side too. In 16 states, there are laws that declare using the purple paint is equivalent to putting up “No Trespassing” signs.

Known as Purple Paint Laws, they are mostly aimed at hunters to alert them that hunting is prohibited in that area. Over 1,000 hunting accidents injure or kill people each year, and property owners want to keep their families, pets, and animals safe, so they paint their posts purple to do so. In fact, there is even a specific paint color used for the posts, aptly called “No Hunting Purple.”

The Purple Paint Law first came about in 1987, when Arkansas passed it. Texas, Illinois, Indiana, Missouri, North Carolina, South Carolina, Tennessee, Maine, Florida, Idaho, Montana, Alabama, Arizona, Pennsylvania and Kansas then followed suit. Many states at first required both signs and paint, but after some time, the local governments felt there was enough awareness of what the paint color meant and no longer required the signage as well.

However, anyone visiting the area might not be aware of the purple posts’ meaning, so it is important for the safety of both landowners and would-be accidental trespassers that word gets out about the significance of purple fence posts.