I have a better idea: update the FlyerTalk Glossary.

In those few forums where this is even an issue, a per-forum announcement can tell people where the "secret decoder ring" is.

Or, you could use a rotating ad banner with "flash cards" ... AA = American Airlines ... NW = NorthWest ... UA = United Airlines ... until they learn them. It's not like we're asking people to memorize the abbreviations for all fifty U.S. states.