The pilot stated that on average he lands on a dirt county road about 15 times per year. On this approach, he did not perform a fly-by of the road to check for hazards. Unknown to him, the road and some signs had been improved since the last time he had landed there. He landed towards the northwest and had a right crosswind from the northeast at about 12-15 miles per hour during the approach. After an uneventful touchdown, he saw a sign on the left side of the road that was not there on any previous flights or landings. He immediately applied right rudder to avoid the sign but the left wing made contact with it. The airplane spun to the left and impacted a dirt berm, which caused the airplane to nose over. The pilot stated that there was no pre-impact mechanical malfunction or failure with the airplane, and that he meant to land on the road.