| Abbreviation | Definition |
|---|---|
| CITU | Citroen |
| CITX | CIT Group |
| CITX | PLM International Incorporated |
| CIW | Illinois Central Gulf (Canadian National Railway) |
| CIW | Illinois Central Railroad Company |
| CIXX | Calciner Industries |
| CIXX | Calciner Industries Incorporated |
| CJPX | General Electric Rail Services Corporation |
| CKIN | Chesapeake and Indiana Railroad |
| CKIX | C.K. Industries |
| CKP | Colorado Kansas and Pacific Railway |
| CKRY | Central Kansas Railway (Kansas and Oklahoma Railroad) |
| CKRY | Central Kansas Railway Incorporated |
| CKSI | Carthage Knightstown and Shirley Railroad |
| CKXU | Cakeboxx Technologies |
| CLC | Columbia and Cowlitz Railway |
| CLC | Columbia and Cowlitz Railway Company |
| CLCO | Claremont and Concord Railway |
| CLCX | Chatahoochee Locomotive |
| CLCZ | Complete Logistics |