Mike Flag
F5. The Reference Layer: Glossary, Units, Signals and Information SourcesDefinition
International Code of Signals letter M, meaning "My vessel is stopped and making no way through the water."
Mike, letter M of the International Code of Signals, means “My vessel is stopped and making no way through the water.” The flag carries a white diagonal cross (saltire) on a blue field. Hoisted singly it tells traffic the ship has no headway, distinct from a vessel underway but stopped for other reasons. It is read alongside the COLREGs definition of a vessel underway, which can be moving or stopped relative to the water.
Source: International Code of Signals (IMO, 1965 edition as amended), single-letter signal M.