WHBM
When it comes to airport designators isn't it a fact that it is relatively simple in the USA, who simply put a K in front of the IATA designator to make the ICAO designator, but not in the rest of the world?
For example Los Angles is LAX in IATA and KLAX in ICAO, San Francisco SFO and KSFO, New York Kennedy JFK and KJFK, and so on.
I prefer the IATA version worldwide because at least in the UK you can often relate the three letters to the airport itself, eg MAN (Manchester), BRS (Bristol), CWL (Cardiff Wales), LBA (Leeds/Bradford), EDI (Edinburgh) and several others, although MME (Teesside that was, I can never fathom its current handle) is a puzzler.