Daymark

A daymark is a navigational aid for sailors and pilots, distinctively marked to maximize its visibility in daylight.

The word is also used in a more specific, technical sense to refer to a signboard or daytime identifier that is attached to a day beacon or other aid to navigation. In that sense, a daymark conveys to the mariner during daylight hours the same significance as does the aid's light or reflector at night. Standard signboard shapes are square, triangular and rectangular; and the standard colours are red, green, orange, yellow and black.