Question

what does this hand signal from a driver mean? slow or stop. right turn. left turn.

Explanation:

In traffic hand - signal rules, when a driver extends the arm straight out of the window (similar to the left - side signal shown in the general understanding of hand signals, assuming the hand is extended to the left as in common signal interpretations), it indicates a left turn. A right - turn hand signal is with the arm bent upwards at the elbow, and a slow or stop signal is with the arm bent downwards at the elbow.

Answer:

Left turn.