| Code | Name | Region |
|---|---|---|
| USMX5 | Mars Hill | ME |
| USYMH | Mars Hill | NC |
| USMR2 | Marseilles | IL |
| USJMA | Marissa | IL |
| USAWK | Mark | IL |
| USAKT | Marked Tree | AR |
| USMKQ | Markesan | WI |
| USMKM | Markham | IL |
| USMKH | Markham | TX |
| USMK5 | Markham | VA |
| USMQL | Markle | IN |
| USVFH | Markleeville | CA |
| USQMK | Markleville | IN |
| USMMS | Marks | MS |
| USZEK | Marksville | LA |
| USMBB | Marlboro | NJ |
| USMBZ | Marlboro | NY |
| US7MA | Marlboro | VT |
| USMXG | Marlboro (marlborough) | MA |
| USUUG | Marlborough | CT |
| USMGX | Marlborough | NH |
| USMB2 | Marlborough, Middlesex | MA |
| USMQH | Marlette | MI |
| USMQM | Marion | AR |
| USMMX | Marion | IA |
| USMWA | Marion | IL |
| USMZZ | Marion | IN |
| US9MN | Marion | KS |
| USIJN | Marion | KY |
| USMN2 | Marion | LA |
| USQAM | Marion | MA |
| USM2R | Marion | MI |
| USMIN | Marion | NC |
| USMXB | Marion | NY |
| USMNN | Marion | OH |
| USXJC | Marion | PA |
| USMSR | Marion | SC |
| USM4R | Marion | SD |
| USMA9 | Marion | TX |
| USXJD | Marion | VA |
| USIMA | Marion | WI |
| USMVF | Marionville | MO |
| USMP8 | Mariposa | CA |
| USISK | Maria Stein | OH |
| USRIA | Marianna | AR |
| USMNF | Marianna | FL |
| USEPC | Maricopa | AZ |
| USAIC | Maricopa | CA |
| USMRI | Mariemont | OH |
| USRL6 | Marienville | PA |