James,
Purple paint is recognized by many people, even in MI.
Problem is, Way too many laws on the books that have to intertwine with law enforcement, insurance, lawyers... Keeping my butt out of jail... as a property owner.
Posting correctly and having law enforcement on your side is a necessity. Otherwise, the family of the drunk who fell in a test hole or other property hazard, could clean you out for the rest of your life! Not kidding at all!
Just the way it is.
