Which of the following is NOT a proper way to signal a left turn?

Waving the left arm up and down is not a proper way to signal a left turn. Standard hand signals for indicating a left turn involve extending the left arm straight out to the side. This signaling method is widely recognized and understood by other drivers and road users.

Using the vehicle's turn signal is also a proper and commonly accepted way to indicate a left turn, as it provides a clear signal to those around you regarding your intended movement. Similarly, extending your left arm straight out is a clear signal to other drivers, indicating that you plan to turn left.

While extending the right arm straight up may indicate a right turn, it is not applicable for signaling a left turn, which further cements why this option is not proper for the intended action. Understanding and utilizing the correct hand signals and vehicle indicators is crucial for safe driving practices.