Indiana House Bill 1233, also known as the "Purple Paint Law," went into effect July 1st

The new law went into effect on July 1. The goal is to make it easier for Indiana landowners to mark their property and prohibit trespassing.

“The Purple Paint marking has to be at least three feet to five feet off the ground, no more than five to the bottom of the marking. The marking has to be at least eight inches long on a tree and one-inch wide.”

http://www.wdrb.com/story/38560286/indiana-purple-paint-law-in-place

here we can mark posts as well as trees as often there are no trees west of Fort Worth , not sure about Indiana

Not a lot of trees here and certainly not around crop land areas.

I have driven through portions of Indiana. Plenty of trees. Many of the fields along the highways have a bit of a treeline along part of the edge. Many of the fields seemed to have tree rows between the different fields.

In PA the row of trees between the fields in common. The farmers threw the stones and rocks from the fields to between the fields and the trees grow up in those rows. It would not surprise me if that is the same in other areas of the country.