“Buick was the first U.S. automaker to offer factory-installed flashing turn signals. Introduced in 1939 as a safety feature, the new-fangled feature was advertised as the ‘Flash-Way Directional Signal’ operated from a switch on the new ‘Handi-shift’ column-mounted shifter. The flashing signals only operated on the rear lights.
“In 1940 Buick enhanced the directional indicators by extending the signals to front lights and adding a self-canceling mechanism.”
Excerpts from http://secondchancegarage.com/public/history-of-turn-signal.cfm . Click on the link to learn about the history of turn signals.
Images: 1939 and 1940 Buick brochure from http://oldcarbrochures.com .
The 1940 Buick was available at dealers in autumn 1939.