What must vessels display to indicate their situation?

Vessels display day shapes to indicate their situation or activity while at anchor or under way during the day. These shapes are standardized signals that communicate important information to other mariners about a vessel's status, such as whether it is at anchor, engaged in fishing, or restricted in its ability to maneuver. The use of day shapes helps ensure safe navigation by allowing other vessels to quickly ascertain the operational state of nearby ships.

For instance, a ball shape indicates a vessel at anchor, while a cylinder typically signifies a fishing vessel that is not under command. The recognition of these shapes is vital for preventing collisions and facilitates situational awareness on the water.

While navigation lights, colored flags, and sound signals all play important roles in marine communication and safety, they serve different purposes. Navigation lights are used at night or in poor visibility conditions to indicate a vessel's position and heading, while colored flags can convey specific information or requests, often relating to communication signals rather than vessel status. Sound signals are used to communicate intentions or warnings but do not provide visual information about a vessel's operational condition. Thus, when it comes to indicating a vessel's situation during the daytime, day shapes are the appropriate visuals to display.