Md. Code, Transportation § 21–606

(a) Except as otherwise provided, each required signal given by hand and arm shall be given from the left side of the vehicle in the manner specified in this section.

(b) A left turn signal is given by the hand and arm extended horizontally.

(c) A right turn signal is given by the hand and arm extended upward; except that a bicyclist may extend the right hand and arm horizontally to the right.

(d) A stop or decrease in speed signal is given by the hand and arm extended downward.