What does it mean if a vessel displays two vertical red lights?

Displaying two vertical red lights indicates that a vessel is aground. This signal is used as part of the navigation rules to alert other mariners to the situation. When a vessel is aground, it means that it is stuck on the bottom and unable to navigate in the water, which can present a hazard to other vessels. The use of two vertical red lights serves as a clear warning to nearby boats to exercise caution when passing, as the vessel is not in a standard operating condition.

Understanding this signal is crucial for safe navigation, as it helps prevent collisions and ensures that other boaters remain aware of potential hazards in the water.