| Code | Name | Region |
|---|---|---|
| USAHX | Marthasville | MO |
| USZAR | Martin | KY |
| USMAN | Martin | MI |
| USQYG | Martin | SC |
| USMMT | Martin | TN |
| USMTN | Martin Mariet/baltimore | MD |
| USZRT | Martindale | TX |
| USMRZ | Martinez | CA |
| USRTI | Martinez | GA |
| USMQP | Martins Creek | PA |
| USMFY | Martins Ferry | OH |
| USMB7 | Martinsburg | OH |
| USAIR | Martinsburg | PA |
| USZEX | Marseilles | OH |
| USM5H | Marshall | AK |
| USKTM | Marshall | AR |
| USQMH | Marshall | CA |
| USML8 | Marshall | IL |
| USMHG | Marshall | MI |
| USMML | Marshall | MN |
| USMHL | Marshall | MO |
| USNMA | Marshall | NC |
| USXRH | Marshall | OK |
| USASL | Marshall | TX |
| USMQ9 | Marshall | VA |
| USQML | Marshall | WI |
| USSL7 | Marshallton | DE |
| USMIW | Marshalltown | IA |
| USM22 | Marshallville | GA |
| USMFB | Marshfield | MA |
| USM46 | Marshfield | ME |
| USMF8 | Marshfield | MO |
| US8FL | Marshfield | VT |
| USML2 | Marlin | PA |
| USM9L | Marlin | TX |
| USM4L | Marlinton | WV |
| US8MR | Marlow | NH |
| USAOW | Marlow | OK |
| USMWE | Marlow Heights | MD |
| USMJT | Marlton | NJ |
| USZRU | Marmaduke | AR |
| USM26 | Marne | IA |
| USQMM | Marne | MI |
| USMUR | Maroa | IL |
| USMQT | Marquette | MI |
| USQTT | Marquette | NE |
| USQEZ | Marquez | TX |
| USMAR | Marrero | LA |
| USMWZ | Marrowbone | KY |
| USXJB | Mars | PA |