Which of these signals indicates a vessel is anchored?

A vessel that is anchored is indicated by the use of a single white light. This is part of the navigation rules that help ensure safe operation on the water, particularly during nighttime or in low visibility conditions. The single white light serves as a clear marker to other vessels that this vessel is not underway, allowing for better navigation and avoidance of collisions.

In contrast, a single red light typically indicates a port side (left side when facing forward) marker in navigation, and two green lights indicate a starboard side (right side) marker. A flashing blue light is generally associated with emergency vehicles or specific regulatory signifying, but it is not a standard signal for indicating that a vessel is anchored.