That is what I was thinking too, Falagar. Seems like an artifact from navtech map data that needs a bit of parsing to work around. It may be an abbreviation for "town of" or similar. Maybe when map data is first read in when creating the db, Twn can be pulled into an optional field or something.
Often, the original towns in New England (and other parts of the country, for that matter) were established as "Townships", sometimes abbreviated "Twn" or "Twp". They were generally laid out as 6 mile by 6 mile square areas (or at least as a 36 square mile area) within a certain survey Township and Range.