Which of the following may be considered a safe water mark?

A safe water mark is a type of navigational aid used in maritime contexts to indicate safe water areas. Each of the mentioned characteristics serves an important purpose in ensuring the safety of vessels navigating through specific waterways.

Vertically striped marks indicate that safe water lies ahead, which can be crucial for helping boat operators determine the course they should take in potentially hazardous waters. The distinct pattern helps in the recognition of the mark and maintains visibility during poor weather or low light conditions.

Spherical shapes are also used as a safe water mark. The round shape can stand out in various environments, providing recognition and helping operators identify safe navigational routes.

Showing a white light is a common feature for navigational aids during the night. This light signals to operators that they are in safe waters, guiding vessels away from potential hazards and ensuring a maximum level of safety while navigating after dark.

When combined, these characteristics represent comprehensive features of safe water marks, enhancing the overall navigation and safety for vessels. Thus, all the elements mentioned are correctly categorized as indicators of safe water, making them collectively the correct answer.