The operator of a vehicle shall, before stopping, turning or changing the course of such vehicle, first see that there is sufficient space to make such movement in safety. If any pedestrian may be affected by the movement of a vehicle stopping, turning or changing its course, the driver of the vehicle shall give a clearly audible signal by sounding the horn. Whenever the operation of any other vehicle may be affected by the movement of a vehicle stopping, turning or changing course, the driver of the vehicle shall give an unmistakable visible signal to the crossing officer, or to the driver of the vehicle following, of his intention to make such movement.
(1958 Code § 16.48)