The Bikini state was an alert state indicator previously used by the UK Ministry of Defence to warn of non-specific forms of threat, including civil disorder, terrorism or war.
Signs giving the current alert state were displayed at the entrance to government buildings and military installations.
The highest levels of alert, Red and Amber, were only intended to be maintained for limited times.
The White state has rarely been used, and is only known to have been used for periods between the Good Friday Agreement of 1998 and 11 September 2001.
The system was illustrated in the British television drama Threads, produced by the BBC in 1984.