Here are 3 Zodiac letters, shown with extreme contrasting done in Photoshop. The Melvin Belli letter of Dec. 20, 1969, on the left, the Z-13 letter of April 20, 1970, in the middle, and the Exorcist letter of Jan. 29, 1974, on the right.

Has anyone posited a reason for these marks?

The Exorcist letter has diagonal creases, pretty much corresponding to the diagonal change in coloring.

I wasn’t able to tell if the other two also had creases, but it is obvious they all have some kind of diagonal marks when they are contrasted.

What do you think?