Similar to Defcon, BIKINI Alert State again has 5 threat levels.
RED: Maximum Threat
AMBER: Heavy Threat
BLACK SPECIAL: Average Threat
BLACK: Minimum Threat
An example of the above system can be found at Y Squadron HQ, QOY. This uses a more traditional British system and reads 'BIKINI Threat Levels: HEIGHTENED'.
Apart from that, Here is an example of a Bikini State: