(1) Numbers, letters, or words on an aid to navigation or regulatory marker shall be placed in a manner to enable them to be clearly visible to an approaching and passing vessel. They shall be block style, well proportioned, and as large as the available space permits. Numbers and letters on red or black backgrounds shall be white; numbers and letters on white backgrounds shall be black.

(2) Odd numbers shall be used to identify solid colored black buoys or black topped buoys; even numbers shall be used to identify solid colored red buoys or red topped buoys. All numbers shall increase in an upstream direction or toward the head of navigation. The use of numbers to identify buoys is discretionary.

(3) Letters only may be used to identify regulatory markers and the white and red vertically striped obstruction markers. When used the letters shall follow alphabetical sequence in an upstream direction. The letters I and O shall be omitted to preclude confusion with numbers. The use of letters to identify regulatory markers and obstruction markers is discretionary.