A safe water mark may be ______.

A safe water mark is designed to indicate that there are navigable waters all around the mark, typically signifying the approach to harbor entrances or the center of a channel. These marks can indeed have various appearances, which is where the options come into play.

A safe water mark can be vertically striped, often in red and white, to enhance visibility and identify it from a distance. Additionally, it can be spherical; specific designs of safe water marks feature a spherical shape atop the navigational aid. The inclusion of a white light is also fundamental to many safe water marks, as it provides visual guidance to mariners, especially during night or reduced visibility conditions.

Considering that all these characteristics can be part of a safe water mark design, the comprehensive answer indicating “all of the above” encompasses the various forms that a safe water mark can take, reinforcing the idea that navigational aids come in different shapes and illumination styles to serve their purpose effectively in maritime navigation.