I have an old entry in my logbook having landed and departed from an airport with identifier PM2. I think I either can't read my handwriting or I made a mistake because I can find no record of such an airport ever existing. Does anyone have a way of finding out?
No. PM2 would not be a valid ID in the FAA system. According to the FAA order defining the system:
1−2−7. ASSIGNMENT SYSTEM §c. Most one−number, two−letter identifiers have been assigned to aviation weather reporting and observation stations and special−use locations. Some of these identifiers may be assigned to public−use landing facilities within the United States and its jurisdictions, which do not meet the requirements for identifiers in the three−letter series. In this identifier series, the number is always in the first position of the three−character combination. (emphasis mine)
So two letters followed by a number is not a valid ID.