What indicates that a driver is making a legal U-turn?

A legal U-turn is indicated by several key factors. First, the driver should ensure that there is a clear lane to perform the turn safely. This means there should be no obstructions or obstacles that could interfere with the maneuver. Second, a sign permitting U-turns is crucial, as it communicates to drivers that such a turn is allowed at that location. Lastly, the absence of incoming traffic is essential for safety, allowing the driver to complete the turn without posing a risk to themselves or other road users. All three of these conditions combined ensure that the U-turn can be executed lawfully and safely.

The other options do not provide sufficient context for a legal U-turn. For instance, another vehicle signaling a U-turn does not indicate the legality of your own turn. Likewise, just having a left turn lane doesn't automatically mean a U-turn is allowed, as the lane might not permit such maneuvers. Lastly, while a green traffic light allows for movement, it doesn’t pertain specifically to the legality of making a U-turn unless combined with other factors.