RCW 46.61.758 Hand Signals
All hand signals required of persons operating bicycles shall be given in the following manner: 1. Left turn. Left hand an arm extended horizontally beyond the side of the bicycle; 2. Right turn. Left hand and arm extended upward beyond the side of the bicycle, or right hand and arm extended horizontally to the right side of the bicycle; 3. Stop or decrease speed. Left hand and arm extended downward beyond the side of the bicycle. The hand signals required by this section shall be given before initiation of a turn. [ed. note: hand signals should only be used when it is safe to remove a hand from the bicycle handlebars.]