| Abbreviation | Definition |
|---|---|
| MARZ | MARTRAC |
| MASX | GE Rail Services |
| MATU | Matson Navigation |
| MATU | Matson Navigation Company |
| MATX | Merchants Investment |
| MATZ | Matson Navigation |
| MATZ | Matson Navigation Company |
| MAW | Maumee and Western Railroad |
| MAW | Maumee and Western Railroad Corporation |
| MAXU | Maxu Containers |
| MAXU | Maxu Containers Limited |
| MAXX | MidAmerican Energy |
| MAXX | MidAmerican Energy Company |
| MAYW | Maywood and Sugar Creek |
| MB | Meridian and Bigbee Railroad (M&B Railroad) |
| MB | Meridian and Bigbee Railroad Company |
| MBBX | Tank Car Services Inc. |
| MBCX | M.B.C.X. Leasing (Chicago Freight Car Leasing) |
| MBCX | Material Brokerage Company |
| MBFX | MBF Industries |