What action is implied by a yellow arrow in a traffic signal?

A yellow arrow in a traffic signal serves as a warning that the protective green arrow is about to end. This signal alerts drivers that they need to prepare to yield or stop as they will be transitioning from a favorable condition for turning (indicated by the green arrow) to a less favorable one. Essentially, the yellow arrow prepares drivers to take necessary actions, such as stopping safely or yielding to oncoming traffic, ensuring that they anticipate changes in the traffic control.

In understanding this, it is important to recognize that the other options do not accurately convey the specific meaning of a yellow arrow. For example, it doesn't indicate an imminent change to green or suggest that stopping is allowed in all directions; rather, it signifies that drivers should begin to yield because the protection of the green arrow is ending.