From Wikipedia, the free encyclopedia:
The ICAO ( /ˌaɪˌkeɪˈoʊ/ , eye-KAY-oh ) airport code or location indicator is a four-letter code designating aerodromes around the world. These codes are defined by the International Civil Aviation Organization, and published in ICAO Document 7910: Location Indicators.
ICAO codes are also used to identify other aviation facilities such as weather stations, International Flight Service Stations or Area Control Centers, whether or not they are located at airports.
These can be found by going here: National Weather Service.
For monitoring Data Buoys at Sea, you will need to use the Station ID for the parameter 'icao', usually a 5 digit code. These can be found by going here: National Data Buoy Center.