nostr:npub1k4qmle0sq0u0fwfz8l7zr85j3ag07z0v3lzj7xrkz5v6sfxdd00ss73lsq nostr:npub19qn6pgk9hs2mg89zg4aujz06meuhmnl9ggapadqkee2vc66dtl2sq46760 
If you care talking about the full code all Canadian airports start with C CYYC. The Y prefix signifies that the airport is co-located with a weather station and the last letters were the Morse Code identifiers from the railway days for the city... 
But yes for twitter it was a short identifier for the city...  
https://en.wikipedia.org/wiki/IATA_airport_code