Final answer:
Extending your left hand straight out the driver's side window typically signals a left turn or lane change. This hand signal provides direction indication especially when turn signals are not working or as an extra alert.
Step-by-step explanation:
If you extend your left hand and aim it straight horizontally out the driver's side window, it usually indicates that you are signaling a left turn or lane change to the left in countries where driving is done on the right side of the road. It is important to use proper hand signals for directional indication, particularly when turn signals are not functioning or to provide an additional visual cue for other drivers. The simplest way to show direction is with relative directions: to the left, to the right, forward, backward, up and down.