What is the light rhythm for Special Marks?

In the IALA Maritime Buoyage System, Special Marks are used to indicate a special feature or area that may not fit the common navigation requirements. The light rhythm for Special Marks can indeed be any variety that is not associated with Cardinal Marks, Isolated Danger Marks, or Safe Water Marks.

Special Marks are distinguished by their unique characteristics which can include a variety of light rhythms not specifically defined by the more standard buoyage categories. This flexibility enables mariners to recognize specific features or areas that require attention, whether they are hazards, recreation areas, or other navigational aids.

By stating that the light rhythm can be "any other than those described in Cardinal, Isolated Danger, and Safe Water Marks," it reflects the purpose of Special Marks—serving diverse navigational needs. This contrasts with other types of marks that have specific, regulated light characteristics meant to convey standardized information clearly to mariners. Therefore, this answer captures the essence and function of Special Marks within the buoyage system, highlighting their distinct role in maritime navigation.