Final answer:
Day shapes must be displayed during daylight hours for maritime navigation purposes, with the practice being tied to the movement of the Sun which sailors use for navigation.
Step-by-step explanation:
Day shapes must be shown during daylight hours. In the context of maritime navigation, day shapes are important for signaling information about a vessel's status and are related to observing the Sun and determining time of day onboard a ship. These shapes are not required between sunset and sunrise when lights are used to convey signals instead. As the Sun's position in the sky changes throughout the day and across seasons, mariners have utilized its path to navigate and tell time, with observations typically centering around noon, when the Sun reaches its highest point in the sky.