Final answer:
The hand signal where a driver's hand and arm are extended straight out indicates a left turn. This is crucial for communication with other road users when vehicle signal lights are not visible or working.
Step-by-step explanation:
When a driver's hand and arm are extended straight out, they are signaling a left turn. This hand signal is one of the basic forms of communication drivers can use to indicate their intentions to other road users when the vehicle's signal lights are not functioning or when visibility is poor. Signaling is an important part of safe driving to alert other drivers and pedestrians of your intended maneuvers.