I'm familiar with that man. That more or less is my definition of entertainment. I think somebody with money and who did it right (billboards on major roads surrounding but not necessarily in front of the court house, never approaching individuals in any way) could get into some interesting legal battles.

Do it right and it is plainly free speech; if I were to write/publish a book instead of design/rent billboards it would be very unambiguously legal. The entertainment comes in the form of seeing how they would try to stop me.