| Abbreviation | Definition |
|---|---|
| SHRX | Kansas City Railroad Museum |
| SHSZ | H and S Railroad |
| SHSZ | H and S Railroad Company Incorporated |
| SHWU | Showa Maritime USA |
| SHWU | Showa Maritime USA Incorporated |
| SHWZ | Showa Line Limited |
| SI | Spokane International Railroad (Union Pacific Railroad) |
| SI | Union Pacific Railroad Company |
| SICX | Sloss Industries Corporation |
| SIEX | Southeastern Industrial Enterprises |
| SIEX | Southeastern Industrial Enterprises Incorporated |
| SIGX | Southern Indiana Gas and Electric |
| SILU | Suttons International |
| SILX | S and I Locomotive Services |
| SIMX | Sierra Bag |
| SIND | Southern Indiana Railway |
| SIND | Southern Indiana Railway Incorporated |
| SIPX | Arrendadora Sipco |
| SIPX | Arrendadora Sipco, S. A. de C. V. |
| SIR | Staten Island Railway |