The pilot reported that, while taking off from a road, the airplane struck a road sign with its left wing. He explained that, during takeoff, the airplane had accelerated rapidly and that, in the next moment, he felt a lurch to the left. The parking brake, which he had forgotten to release, then released. He added that he had "incorrectly assumed" that the brake had grabbed and caused the lurch, not the unknown to him, sign strike. Subsequently, he corrected with rudder and continued the flight. He added that the airplane flew "normally" but that it had a "slightly left-wing heavy feel." He continued the flight without further incident. Postaccident examination of the airplane revealed that it had sustained substantial damage to the left wing. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.