Signals. (a) The operator of any vehicle upon a highway shall, before starting, stopping or turning from a direct line, first see that the movement can be made in safety and, if any pedestrian may be affected by the movement, shall give a clearly audible warning signal, and shall give a signal, as required in this section, to indicate an intention to make such movement. (b) Any stop or turn signal required by this section shall be given either by means of the hand and arm, by signal lights, or by a mechanical signal device that clearly indicates to both approaching and following traffic an intention to turn right or left. Any motor vehicle in use on a highway, however, shall be equipped with, and the required signal shall be given by, signal lights or a mechanical signal device where the distance from the center of the top of the steering post to the left outside limit of the body, cab, or load of the motor vehicle exceeds 24 inches, or where the distance from the center of the top of the steering post to the rear limit of the body of the motor vehicle exceeds 14 feet, whether a single vehicle or a combination of vehicles. (c) Any stop or turn signal required by this section shall be given either by means of the hand and arm, or by a signal light or mechanical signal device, but when a vehicle is so constructed or loaded that a hand-and-arm signal would not be visible both to the front and rear of such vehicle then the signals must be given by a light or signal device. (d) All signals required by this section, when given by hand and arm, shall be given from the operator’s side of the motor vehicle in the following manner, and the signals shall indicate as follows: (1) Left turn, hand and arm extended horizontally; (2) Right turn, hand and arm extended upward; (3) Stop or decrease speed, hand and arm extended downward. Source: PL 3-61, § 1 (§ 537).