Missouri Revised Statutes Title XIX. Motor Vehicles, Watercraft and Aviation § 304.019. Hand and mechanical signals, violations, penalty

(1) An operator or driver when stopping, or when checking the speed of the operator's vehicle, if the movement of other vehicles may reasonably be affected by such checking of speed, shall extend such operator's arm at an angle below horizontal so that the same may be seen in the rear of the vehicle;

(2) An operator or driver intending to turn the operator's vehicle to the right shall extend such operator's arm at an angle above horizontal so that the same may be seen in front of and in the rear of the vehicle, and shall slow down and approach the intersecting highway as near as practicable to the right side of the highway along which such operator is proceeding before turning;

(3) An operator or driver intending to turn the operator's vehicle to the left shall extend such operator's arm in a horizontal position so that the same may be seen in the rear of the vehicle, and shall slow down and approach the intersecting highway so that the left side of the vehicle shall be as near as practicable to the center line of the highway along which the operator is proceeding before turning;

(4) The signals herein required shall be given either by means of the hand and arm or by a signal light or signal device in good mechanical condition of a type approved by the state highway patrol; however, 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 such signals shall be given by such light or device. A vehicle shall be considered as so constructed or loaded that a hand and arm signal would not be visible both to the front and rear when the distance from the center of the top of the steering post to the left outside limit of the body, cab or load exceeds twenty-four inches, or when the distance from the center of the top of the steering post to the rear limit of the body or load thereon exceeds fourteen feet, which limit of fourteen feet shall apply to single vehicles or combinations of vehicles. The provisions of this subdivision shall not apply to any trailer which does not interfere with a clear view of the hand signals of the operator or of the signaling device upon the vehicle pulling such trailer; provided further that the provisions of this section as far as mechanical devices on vehicles so constructed that a hand and arm signal would not be visible both to the front and rear of such vehicle as above provided shall only be applicable to new vehicles registered within this state after the first day of January, 1954.