Some small uncontrolled airports have "K" identifiers such as KPHK (Palm Beach County Glades) "Pahokee". Others such as 42M (Thayer Mem) "Thayer" have a numeric identifier. Both have 122.9 CTAF listed. Pahokee is Class G, Thayer is E.
My question is how is an "E" airport distinguished from a "G" airport on the basis of the identifier?