What to do.........

Agree on the "No Trespassing" sign.

I would get good and liquored up, gas up your Mopar, and pull several WOT passes up and down his street to get his attention. Make sure it's either early in the morning or late at night. Once he's out of the house, you can pull one more pass and come sliding into his front yard sideways. Toss him a beer and without asking, just start picking through his cars. He'll be speechless.