A gang of 15 men from across London's underworld stopped a train by turning the signal red, brutally coshed the driver and made off with ￡2.6m (then $7.3m) in cash from the mail cars.
The red/black concept, sometimes called the red-black architecture
or red/black engineering,
refers to the careful segregation in cryptographic systems of signals that contain sensitive or classified plaintext information (red signals) from those that carry encrypted information, or ciphertext (black signals).