If you’re in Missouri or Illinois and come across a purple fence, turn around. Here's why.

Missouri and Illinois are two of only 11 states in the country with the “Purple Paint Law” according to a story at AWM.com. Essentially, a fence or line of trees painted bright purple is the equivalent of a giant “NO TRESPASSING” sign. Though the symbol certainly resonates closely with hunters (the special paint is even called “No Hunting Purple”) it is important to note that the trespassing ban applies to all.

As signs can be damaged or blown away, the purple paint code serves as a more effective (and cheaper) alternative to landowners.

Other states with the “Purple Paint Law” include Texas, North Carolina, Florida, Idaho, Arkansas, Montana, Arizona, and Kansas. Missouri adopted the law in 1993 and Illinois in 2011.

The law was first enacted in Arkansas in 1987 and signed by then Governor Bill Clinton.