"People who are going places use turn signals!"

Few sites of interest:

P.U.T.S.: Please Use Turn Signals!
One of these rules (since the late 1950s) is the use of turn signals to indicate your intention to make a movement on the road, street or highway...

Didn’t use your turn signal? That’ll be $1050, please!
-get a ticket for jaywalking or speeding, and now ‘reckless driving’ for failing to use a turn signal, can be interpreted as “a danger to himself or others” ...

Howstuffworks "How Turn Signals Work"
To most drivers, turn signals seem pretty simple: There’sa lever that makes your signal lights flash. But there’s actually some cool technology at work.