I've seen a few fence posts that had a rather peculiar color on the top and never knew what it meant until now. The color in question is purple and if you see it on a the top of a fence post in Missouri or Illinois, you need to turn around immediately and leave. It's a law.

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Are you familiar with the purple fence post law? It's a law in both Missouri and Illinois. Pro Tip: it also works on trees.

What does purple paint on a tree or fence post mean?

In both Missouri and Illinois, it means no trespassing. The concept of why laws and statutes like this were passed were to give property owners and easy way to mark their property without having to spend a small fortune on signs.

In Illinois, the law is very specific. Property owners must make sure their purple markings are at least 8 inches in length if it's a vertical line or at least the top 2 inches if it's the top of a fence post. You're also expected to leave no more than 36 feet apart so anyone approaching your property can easily spot it.

There's a little more leeway in Missouri as the purple markings can be up to 100 feet apart.

What happens if a person crosses an area where there are purple markings?

In Illinois, it's a Class B misdemeanor according to the state website.

The whole point of this is if you see purple markings, you're about to enter a place you shouldn't be without permission. It's the law.

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