Abstract: A robotic sign waver has a chassis including a main plate which mounts a drive train. The drive train includes a motor and a gearbox coupled to the motor. The gearbox has an output shaft that drives a crank arm with a linkage rod attached thereto. The linkage rod drives a rocker plate that is mounted on the main plate for repetitive motion. An elongated waving arm is mounted on the rocker plate for repetitive motion with the rocker plate. The rocker plate is robust to withstand the stress and wear of repetitive motion while the waving arm is relatively light to minimize its load on the drive train. A counterweight is attached to the rocker plate on the opposite side of the main plate from the rocker plate by means of connectors extending through slots in the main plate. A reversible connector plate allows attachment of the chassis to either vertical or angled sign boards.