Codes for other large cities are usually well known, at least by people who live in the area or fly to the city frequently, yet are not really used as words. Few people, including those in the travel industry, would say that they wanted to fly to P-D-X (Portland, Ore.) or to P-W-M (Portland, Me.).
|FAT - read the article to find out what that is|
Some codes are logically derived from the name of the city (SEA for Seattle) or the airport (LGA for LaGuardia in New York City) but others seem bizarre, usually because they are derived from the airfield which was named after a now obscure aviator or other personage (GEG for Spokane's Geiger Field; BDL for Hartford's Bradley Field).
For your airport code pleasure here's an article written by Rick Seaney, who is the founder of the FareCompare website. Entitled "The Wacky Logic Behind Airport Codes", it's a fun piece that draws back the veil on some of the reasons behind the 3-letter "names" of airports.
I used to think I was pretty good at the 3-letter code game but I sure wouldn't want to match wits with Rick Seaney.