What does three red lights in a row indicate?

The correct interpretation of three red lights in a row is that it signals "No room above." This indication is commonly used in maritime contexts to inform vessels that there is no space available for another craft to safely navigate, particularly in situations such as when using a crane or during cargo operations where overhead obstructions may pose a risk. The use of three red lights visually conveys a clear warning to keep other vessels at a safe distance, ensuring safe operations and preventing potential accidents.

Understanding this signal is particularly important for the safety of navigation and anchorage situations, as it helps to manage congestion and maintain safe distances in areas where vessels are operating with limited vertical clearance.