The pilot reported that he had flown the approach at a shallow angle causing him to lose sight of the runway lighting system during the landing flare. During the flare the airplane drifted to the left resulting in the left main landing gear touching down in the dirt next to the runway. Subsequently the airplane veered to the left, and struck a runway sign. The pilot reported that he was unaware that he had struck the sign and was able to correct back to the center of the runway. The remainder of landing roll and taxi were uneventful. The damage to the underside of the left wing and the sign was not found until the following day. The pilot reported that there were no known mechanical malfunctions or failures prior to the accident.