The light signal, consisting of a flashing blue light as defined in the Airworthiness Technical Manual of the International Civil Aviation Organisation (ICAO) Doc. 9051, is established for the use of medical aircraft to signal their identity. No other aircraft shall use this signal. Medical aircraft using the flashing blue light should exhibit such lights as may be necessary to make the light signal visible from as many directions as possible.

In accordance with the provisions of Chapter XIV, para. 4 of the International Maritime Organisation (IMO) International Code of Signals, vessels protected by the Geneva Conventions of 1949 and the Protocol should exhibit one or more flashing blue lights visible from any direction.

Medical vehicles should exhibit one or more flashing blue lights visible from as far away as possible. The High Contracting Parties and, in particular, the Parties to the conflict which use lights of other colours should give notification of this.

The recommended blue colour is obtained when its chromaticity is within the boundaries of the International Commission on Illumination (ICI) chromaticity diagram defined by the following equations:

The recommended flashing rate of the blue light is between sixty and one hundred flashes per minute.