The private pilot was attempting a soft field takeoff on a paved runway. He advanced the throttle to the full forward position, applied full back pressure on the flight controls, and proceeded down the runway. The airplane veered to the left and the pilot attempted to counteract the veer by applying right rudder. The pilot then elected to reject the takeoff. He retarded the throttle and lowered the nose of the airplane. The airplane exited the runway and struck a frangible airport sign. Representatives from the Federal Aviation Administration reported no mechanical malfunctions with the airplane that would have precluded normal operation. The forward spar of the horizontal stabilizer was bent aft during the accident sequence.