"In broadcasting and radio communications, a call sign (also known as a callsign, callname or call letters, or abbreviated as a call) is a unique designation for a transmitting station. In some countries they are used as names for broadcasting stations, but in many other countries they are not. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or even cryptographically encoded to disguise a station's identity" (Wikipedia).
|NPM||Navy radio Wailupe, east of Honolulu, Hawaii|
|NPU||Navy radio Tutuila, Samoa|
|NRUI2||HF/DF station on Howland|