Which of the following is a characteristic of a safe water mark?

A safe water mark is characterized by its primary purpose of indicating that there is safe water on all sides of the mark, making it particularly useful for navigational purposes. One of its distinguishing features is that it often has a flashing white light. This characteristic aids mariners in identifying the buoy during nighttime or in poor visibility conditions, providing them with crucial navigational information.

The other options describe features that belong to different types of buoys or marks. For instance, horizontal red bands are typical of a lateral mark, specifically a port hand buoy. The color green is used for starboard hand buoys, which also aids in lateral navigation. Solid yellow coloration is characteristic of special marks that indicate a specific area or feature but do not necessarily imply safe water. Thus, the correct answer emphasizes the importance of the flashing white light as a navigational aid associated with safe water marks.