All signals herein required given by hand and arm shall be given from the left side of the vehicle in the following manner and such signals shall indicate as follows:
         1. Left turn – Hand and arm extended horizontally.
         2. Right turn – Hand and arm extended upward, except
    
that a person operating a bicycle may extend the right hand and arm horizontally and to the right side of the bicycle.
        3. Stop or decrease of speed – Hand and arm extended
    
downward.