According to the United States Coast Guard, the red triangular daymark indicates that the structure is a day beacon. Day beacons are unlighted towers or poles that are painted or otherwise marked with a distinctive color or colors. The purpose of a day beacon is to provide a day reference point for navigation.
The red triangular daymark is one of the most common daymarks used by the Coast Guard. It is used to mark navigational hazards, such as shoals, reefs, and rocks. It is also used to mark the location of navigational aids, such as buoys and lights.
The red triangular daymark is easy to spot during the day, and it is especially useful in foggy or cloudy conditions. It is important to note that the red triangular daymark is not meant to be used at night.