A

David

Darling

semaphore

A semaphore is a device or technique that communicates messages visually. It is a type of optical telegraph. A railway semaphore signal consists of a vertical post on which a single projecting arm is mounted, whose angle indicates 'all clear' or 'danger'. In flag semaphore, a signaler indicates letters and numerals by the position of his outstretched arms, emphasized with flags.