Electric turn-signals date from as early as 1907 when Percy Douglas-Hamilton applied for a patent (received in 1909 as U.S. patent 912831) for a device "indicating the intended movements of vehicles". Hand signals were simulated so that other drivers, accustomed to reading hand signals, would understand their meaning. A more modern style using flashing lights to indicate a turn was patented in 1938 (see U.S. patent 2,209,780 which looks very familar to today's signals, and similar U.S. patents 2,204,096 and 2,201,657, 2,114,731, 2,186,766, also filed in 1938). The first flashing electric turn signal was offered on the 1938 Buick as a new safety feature. Buick advertisments hailed it as a “Flash-Way Directional Signal.” Buick added a self-canceling mechanism in 1940 that was attached to the steering column.
When turn-signal functionality is provided by multiple lit elements that illuminate sequentially rather than simultaneously, it is called a "sequential turn signal." This created a visual effect of outward motion in the direction of the intended turn or lane change. Sequential turn signals were first factory fitted to 1965–1971 model year Ford Thunderbirds and have been affectionately referred to as "T-Bird Turn Signals."
In the 1965-1968 Ford-built cars (and 1971–1972 Nissan Cedrics), an electric motor drove, through reduction gearing, a set of three slow-turning cams that actuates switches to turn on the lights in sequence. A very throughout guide to the original turn signal systems, and how to service them, can be found in an article titled '65-’66 Sequentials. Later cars used a transistorized control module with no moving parts to wear, break, or go out of adjustment.
In time, most major automobile manufacturers offered flashing turn signal and today most countries require turn signals on all new vehicles that are driven on public roads. An in-depth article on the history of turn signals can be found in an article titled Turn, Turn, Turn: A History of the Turn Signal.