| 1 | MMI | Marina Militare Italiana | Callsign: Italian Navy, | I | AVCODES |
| 2 | MMIA | MULTI-MERCHA | | | SCAC4 |
| 3 | MMIC | MARINE & MARKETING INTER CORP | | | PWRC |
| 4 | MMID | Maryland Midland Ry., Inc. | added 1/1984; 1/1994-7/2005 | | NAKINA |
| 5 | MMID | Maryland Midland Ry. Co. | added 1/1981; added 4/1981; eliminated 1/1984 | | NAKINA |
| 6 | MMID | Maryland Midland Ry., Inc. | added 1/81; added 4/81; 1/94-7/2000 | | NRHS |
| 7 | MMID | MARYLAND MIDLAND RAILWAY, INC. | | | PWRC |
| 8 | MMID | Maryland Midland Railway | | | RSRV |
| 9 | MMID | Maryland Midland | | USA | TRAFFIC |
| 10 | MMIE | M & M INC | | | SCAC4 |
| 11 | MMIF | MEK MOBILITY INC | | | SCAC4 |
| 12 | MMIH | MOULDER, MICHAEL | | | SCAC4 |
| 13 | MMII | MONAM INDUSTRIES INC | | | SCAC4 |
| 14 | MMIJ | MAXZA MATERIALS INC | | | SCAC4 |
| 15 | MMIK | MONK, MICHAEL | | | SCAC4 |
| 16 | MMIN | MCMILLEN RANCHING LTD | | | SCAC4 |
| 17 | MMIO | MONDORO MARINE INC | | | SCAC4 |
| 18 | MMIP | MUMA MANUFACTURING INC | | | SCAC4 |
| 19 | MMIQ | MALCOLM MARINE INC | | | SCAC4 |
| 20 | MMIRL | Mini Maritza-Iztok EAD / Мини Марица-Изток ЕАД | | BG | VKM |
| 21 | MMIT | MOVE MANAGEMENT INTERNATIONAL INC | | | SCAC4 |
| 22 | MMIU | JSC METALLURGMONTAZH | | | SCAC4 |
| 23 | MMIX | Metal-Matic, Inc. | added 7/1973; 1/1975-1/1980; eliminated 4/1984 | | NAKINA |
| 24 | MMIX | Metal-Matic, Inc. | added 7/73; 1/75-1/80; eliminated 4/84 | | NRHS |
| 25 | MMIX | METAL-MATIC, INC. | | | PWRC |
| 26 | MMIY | MARQUEZ, MIKE | | | SCAC4 |
| 27 | MMIZ | MONTANA MERCHANDIZING INDUSTRY | | | PWRC |
