| Abbreviation | Railroad Name |
| MACK | Mack Railbus
|
| MBPX | MacMillan-Blodell Inc.
|
| MAERSK | Maersk
|
| MAGMA | Magma Arizona
|
| MEC | Maine Central
|
| MOW | Maintenance Of Way
|
| MS | Management Service
|
| MANN | Manistee & Northeastern
|
| MANR | Manistee & Repton
|
| MAQL | Manistique & Lake Superior
|
| MPP | Manitou & Pikes Peak
|
| MJ | Manufacturers Junction Railway
|
| MSR | Manufacturers Railway
|
| MSRY | Manufacturers Railway, St Louis
|
| MOL | Marcellus & Otisco Lake
|
| MARB | Marianna & Blountstown
|
| MTW | Marinette, Tomahawk & Wstrn
|
| MARKL | Marklin |
| MAPA | Maryland & Pennsylvania
|
| MRYM | Maryland Midland
|
| MASONITE | Masonite
|
| MBTA | Massachusetts Bay Trans.
|
| MSCX | Mather Stock Car Express
|
| MATHIESON | Mathieson Dry Ice Cars
|
| MATSON | Matson
|
| MAXSON | Maxson
|
| MCR | Mccloud River
|
| MACO | Mccormick Ashland City & Nash.
|
| MKC | Mckeesport Connecting
|
| MEADOW RIV | Meadow River Lumber
|
| MEDCO | Medco Lumber, Oregon
|
| MDTC | Merchant Dispatch Trans.
|
| MBR | Meridian & Bigbee River
|
| METRA | Metra
|
| MN | Metro North
|
| ML | Metrolink
|
| MTA | Metropolitan Transit Authority
|
| MICCAL | Michigan California Lumber
|
| MICEN | Michigan Central NYC
|
| MMRR | Mid - Michigan
|
| MRR | Mid Atlantic
|
| MSRC | Mid South
|
| MIDDLE CRE | Middle Creek
|
| MIDDLE FOR | Middle Fork
|
| MDLU | Middletown & Unionville
|
| MIDLAND CN | Midland Continental
|
| MIDLAND TE | Midland Terminal
|
| MIDLAND VA | Midland Valley
|
| MDR | Midlouisiana Rail
|
| MIDWEST | Midwest Grain
|
| MWM | Midwest Quarry & Mining Co.
|
| AIR FORCE | Military: Air Force
|
| ARMY | Military: Army
|
| NAVY | Military: Us Navy
|
| MILSTEAD | Milstead
|
| MILWHW | Milwaukee Hiawatha |
| MILW | Milwaukee Road
|
| MINARETS | Minarets Lumber
|
| MINERAL RN | Mineral Range
|
| MSPSSM | Minn., St. Paul&sault Ste. Marie
|
| MSTL | Minneapolis & St Louis
|
| MNS | Minneapolis Northfield & Sthrn
|
| MNRR | Minnesota Commercial
|
| MCP | Minnesota Corn Processors
|
| MDW | Minnesota Dakota & Western
|
| MINN WESTE | Minnesota Western
|
| MISSABE | Missabe
|
| MIAL | Mississippi & Alabama
|
| MISV | Mississippi & Skuna Valley
|
| MSC | Mississippi Central
|
| MSDR | Mississippi Delta
|
| MSE | Mississippi Export
|
| MISS EXPOR | Mississippian
|
| MOAR | Missouri & Arkansas
|
| MI | Missouri Illinois
|
| MP | Missouri Pacific (MP)
|
| MKT | Missouri, Kansas & Texas
|
| MNVA | Mnva Railroad
|
| MOBIL | Mobil Oil
|
| MBGULF | Mobile & Gulf
|
| MET | Modesto & Empire Traction
|
| MGA | Monogahela
|
| MON | Monon
|
| MRL | Montana Rail Link
|
| MONT WESTE | Montana Western
|
| MTWS | Montana, Wyoming & Southern
|
| MONTOUR | Montour
|
| MMA | Montreal Maine & Atlantic
|
| MOORE CENT | Moore Central
|
| MORRELL | Morrell Meat Packing
|
| MERIE | Morristown & Erie
|
| MCSA | Moscow Camden&Sanaugustine
|
| MOSHASSUCK | Moshassuck Valley
|
| MOUNT HOPE | Mount Hood
|
| MOUNT HOOD | Mount Hope Mineral
|
| MPCX | MPCX
|
| MPI | MPI Leasing
|
| MPSX | MPSX
|
| MRMX | MRMX
|
| MTH | MTH Line
|
| MUL | Multromah
|
| MUNW | Muncie & Western
|
| MRSF | Municipal Rly Of San Fran. (elec)
|
| MUN | Murfreesboro-nashville
|
