What is the day shape for a black ball used for anchoring?

The day shape for a black ball is used to indicate that a vessel is at anchor. This shape is recognized internationally and is part of the maritime signaling system. When you see a black ball displayed during the day, it serves as a clear and simple visual indication to other vessels that the anchored vessel is not moving and it helps prevent collisions.

The other shapes listed, such as the cube, cone, and rectangle, do not represent anchoring and lack the significance that the black ball conveys in maritime communication. Understanding these shapes and their meanings is crucial for safe navigation and ensuring that vessels are aware of each other's status on the water.