No driver of a vehicle shall suddenly start, slow down, start or attempt to turn without first giving a suitable signal in such a manner as to apprise others who might be affected by his action.
   The signals herein required shall be given either by means of the hand and arm or by a signal lamp or other device, but when a vehicle is so constructed or loaded that hand and arm signal would not be visible both to the front and rear of such vehicle when said signals must be given by such a lamp or device.
   All signals herein required, given by hand and arm signal, shall be given from the left side of the vehicle in the following manner and such signals shall indicate as follows:
   Left turn - hand and arm extended horizontally.
   Right turn - hand and arm extended upward or moved with a sweeping motion from rear to the front.
   Stop or decrease of speed - hand and arm extended downward.