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 and 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.