Title 40, Chapter 6, Section 124
(a) Any stop or turn signal when required in this chapter shall be
given either by means of the hand and arm or by signal lights,
except as otherwise provided in subsection (b) of this Code section.
(b) Any motor vehicle in use on a highway shall be equipped with,
and a required signal shall be given by, signal lights when the
distance from the center of the top of the steering post to the left
outside limit of the body, cab, or load of such motor vehicle
exceeds 24 inches or when the distance from the center of the top of
the steering post to the rear limits of the body or load thereof
exceeds 14 feet. The latter measurement shall apply to any single
vehicle and also to any combination of vehicles.