Echo Flag
F5. The Reference Layer: Glossary, Units, Signals and Information SourcesDefinition
International Code of Signals letter E, meaning "I am altering course to starboard."
Echo, letter E of the International Code of Signals, means “I am altering my course to starboard.” The flag is split horizontally, blue over red. Flown singly it is a maneuvering signal and complements India (course to port). Watchkeepers read Echo alongside the COLREGs sound signals (one short blast for a starboard alteration) when communicating intended course changes in sight of one another.
Source: International Code of Signals (IMO, 1965 edition as amended), single-letter signal E.