Note: Marks ending in U are for container owners; marks ending in X are not common carriers; marks ending in Z are for trailers without flanged wheels. All other marks are of common-carrier railroads.

S

• SA - Savannah and Atlanta Railroad; Central of Georgia Railroad
• SAL - Seaboard Air Line Railway; Seaboard System Railroad; CSX Transportation
• SAMX - Cargill, Inc. (Seaboard Allied Milling Department)
• SAN - Sandersville Railroad
• SANX - San Angelo Tank Car Line
• SAPT - Savannah Port Terminal Railroad
• SATX - City Public Service Board of San Antonio
• SAUX - Sauvage Gas Company
• SAWX - Sawco, Inc.
• SAZX - Saz Transportation Corporation
• SB - South Buffalo Railway
• SBC - Ferrocarril Sonora Baja California
• SBD - Seaboard System Railroad; CSX Transportation
• SBGX - Industry Financial Corporation
• SBIX - Standard Brands, Inc.
• SBK - South Brooklyn Railway
• SBLN - Sterling Belt Line Railway
• SBLX - Sunbelt/Chlor/Alkali Partnership
• SBM - St. Louis, Brownsville and Mexico
• SBVR - South Branch Valley Railroad
• SC - Sumter and Choctaw Railway
• SCAX - Southern California Regional Rail Authority (Metrolink)
• SCBG - Santa Cruz, Big Trees and Pacific Railway
• SCCX - Shell Oil Company
• SCEX - Southern California Edison
• SCFE - South Central Florida Railroad
• SCFS - Straits Car Ferry Service Corporation
• SCGX - Schuler Grain Company; Eades Commodities
• SCHX - Stauffer Chemical Company
• SCJX - Gulf Oil Products Company; Chevron Phillips Chemical Company
• SCL - Seaboard Coast Line Railroad; Seaboard System Railroad; CSX Transportation
• SCLX - Spielman & Caddell Leasing
• SCM - Strouds Creek and Muddlety Railroad
• SCMX - Shell Oil Company
• SCOX - Scoular Bishop Grain Company
• SCPX - Shell Oil Company
• SCR - SCR
• SCRW - Seaway Commercial Railway
• SCST - Seaboard Transportation Company (subsidiary of Seaboard Coast Line Railroad)
• SCT - Sioux City Terminal Railway
• SCTR - South Central Tennessee Railroad
• SCWX - South Carolina Public Service Authority
• SCXF - South Central Florida Express, Inc.
• SCXY - St. Croix Valley Railroad
• SCYX - Farmers Cooperative Association of York, Nebraska
• SDA - San Diego and Arizona Railway
• SDAE - San Diego and Arizona Eastern Railway
• SDCX - AMAX Chemical Corporation
• SDER - San Diego Electric Railway
• SDEX - Swindell-Dressler Energy Supply Company
• SDIV - San Diego and Imperial Valley Railroad (expired)
• SDIY - San Diego and Imperial Valley Railroad
• SDNX - North County Transit District
• SDPX - South Dakota Soybeen Processors
• SDRX - Sounder commuter rail
• SE - Ferrocarriles Unidos del Sureste
• SECX - South-East Coal Company
• SEIX - Seimax Gas Corporation
• SEMX - Seminole Electric Cooperative
• SEPA - SEPTA
• SEPX - Southwestern Electric Power Company
• SERA - Sierra Railroad
• SERX - ACF Industries (Shippers Car Line Division)
• SFIX - System Fuels, Inc.
• SFLC - Atchison, Topeka and Santa Fe Railway; BNSF Railway
• SFLR - Shore Fast Line Railroad
• SFPP - Spruce Fall Power and Paper
• SFQ - Atchison, Topeka and Santa Fe Railway; BNSF Railway End Of Train Devices
• SFRB - Atchison, Topeka and Santa Fe Railway (Santa Fe Refrigerated Despatch)
• SFRC - Atchison, Topeka and Santa Fe Railway (Santa Fe Refrigerated Despatch)
• SFRD - Atchison, Topeka and Santa Fe Railway (Santa Fe Refrigerated Despatch)
• SFRE - Atchison, Topeka and Santa Fe Railway (Santa Fe Refrigerated Despatch)
• SFRP - Atchison, Topeka and Santa Fe Railway (Santa Fe Refrigerated Despatch)
• SFSR - Santa Fe Southern Railway
• SFSX - San Francisco Transportation Services Company
• SFTX - Continental Tank Car Corporation
• SGAX - SGA Leasing Company
• SGCX - Sungas Corporation of Florida
• SGIX - LPG Transportation, Inc.
• SGLR - Seminole Gulf Railway
• SH - Steelton and Highspire Railroad
• SHLX - Procor Ltd.
• SHPX - American Industrial Transport, formerly ACF Leasing/Shippers Car Line Division
• SHQX - American Industrial Transport
• SHRX - Kansas City Railroad Museum
• SI - Spokane International Railroad; Union Pacific Railroad
• SIGX - Southern Indiana Gas and Electric Company
• SIMX - Sierra Bag Company
• SIND - Southern Indiana Railway
• SIRC - Staten Island Railway
• SIRR - Southern Industrial Railroad
• SIRX - Southern Illinois Railcar Corporation
• SJFX - Western Fuels & Asphalt Supply, Inc.; GLNX Corporation
• SJMX - St. Joe Minerals Corporation
• SJRT - St. Johns River Terminal
• SJT - St. Joseph Terminal Railroad
• SJVR - San Joaquin Valley Railroad
• SKCX - ARCO Chemical Company
• SKNX - Saskatchewan Grain Car Corporation
• SKOL - South Kansas and Oklahoma Railroad
• SKPX - Saskatchewan Grain Car Corporation
• SKSX - Safety-Kleen Systems, Inc.
• SKTX - Ski Train
• SL - Salt Lake City Southern Railroad
• SLAW - St. Lawrence Railroad
• SLAX - St. Lawrence Starch Company, Ltd.
• SLC - San Luis Central Railroad
• SLGG - Sidney and Lowe Railroad
• SLGW - Salt Lake, Garfield and Western Railway
• SLH - Sugarloaf and Hazelton Railroad
• SLOX - Selox, Inc.
• SLR - St. Lawrence and Atlantic Railroad
• SLRG - San Luis and Rio Grande Railroad
• SLRX - Southern Locomotive & Railcar
• SLSF - St. Louis - San Francisco Railway (Frisco); Burlington Northern Railroad
• SLWC - Stillwater Central Railroad
• SLTX - Slade Transport, Inc.
• SM - St. Mary's Railroad
• SMA - San Manuel Arizona Railroad
• SMCX - San Miguel Electric Cooperative
• SMEX - South Mississippi Electric Power Association
• SMMX - St. Mary's Cement Company
• SMPX - Stone Mountain Scenic Railroad
• SMRR - Sisseton Milbank Railroad
• SMNX - Solvay Minerals, Inc.
• SMRX - Southeastern Railway Museum
• SMV - Santa Maria Valley Railroad
• SN - Sacramento Northern Railway
• SNBL - Sioux City and New Orleans Barge Line
• SNCT - Seattle and North Coast Railroad
• SNFX - IND/AG Chemicals, Inc.
• SNHX - IND/AG Chemicals, Inc.
• SNJX - New Jersey Transit RiverLINE work train
• SOEX - Shell Oil Company
• SOGX - Diamond Shamrock Chemicals Company
• SOIX - Sand Seed Service, Inc.
• SOLX - Solano Rail Car Company
• SOM - Somerset Railroad
• SOO - Soo Line Railroad; Canadian Pacific Railway
• SOPR - South Pierce Railroad
• SOR - Southern Ontario Railway
• SOU - Southern Railway; Norfolk Southern Railway
• SP - Southern Pacific Railroad; Union Pacific Railroad
• SPAX - SEPTA
• SPCX - SPC Rail Group LLC
• SPEG - Spencerville and Elgin Railroad
• SPFE - Pacific Fruit Express; Southern Pacific Railroad; Union Pacific Railroad
• SPGX - Suburban Propane
• SPMW - Southern Pacific Railroad; Union Pacific Railroad (maintenance of Way)
• SPQ - Southern Pacific Railroad; Union Pacific Railroad End Of Train Devices
• SPS - Spokane, Portland and Seattle Railway; Burlington Northern Railroad
• SPSX - Progress Rail Services
• SPUD - St. Paul Union Depot Company
• SQVR - Sequatchie Valley Railroad
• SRAX - Southern Rail Associates, Inc.
• SRC - Strasburg Railroad
• SRCX - Sid Richardson Carbon Company
• SRIX - Southern Region Industrial Realty, Inc.; Southwest Rail Industries, Inc.
• SRL - Swift Refrigerator Lines (expired)
• SRLX - General American Transportation Corporation
• SRN - Sabine River and Northern Railroad
• SROX - United States Department of Energy (Savannah River Operations Office)
• SRPX - Salt River Project Agricultural Improvement and Power District
• SRRX - Star Railroad Equipment
• SRY - Southern Railway of British Columbia
• SS - Sand Springs Railway
• SSAM - Sault Ste. Marie Bridge Company (subsidiary of Wisconsin Central)
• SSDK - Savannah State Docks Railroad
• SSGX - McMaster Grain Company
• SSH - South Shore Railroad
• SSR - S&S Shortline
• SSEX - Radius Recycling (Schnitzer Steel Industries)
• SSIX - Itel Corporation
• SSW - St. Louis Southwestern Railway (Cotton Belt); Southern Pacific Railroad; Union Pacific Railroad
• ST - Springfield Terminal Railway; Boston and Maine Railroad; Pan Am Railways
• STAX - Stauffer Chemical Company; OCI Chemical Corporation
• STC - Simpson Timber Company
• STCX - Sterling China Company
• STE - Stockton Terminal and Eastern Railroad
• STER - St. Thomas and Eastern Railway
• STEX - Sterling Chemicals, Inc.
• STLE - St. Louis & Evansville Railroad Co.
• STLX - A. E. Staley
• STMA - St. Maries River Railroad
• STMX - A. E. Staley
• STOX - ACF Industries
• STRC - Stuart Chemical Transportation
• STRT - Stewartstown Railroad
• STRX - St. Regis Paper Company
• STSX - A. E. Staley
• STTX - Trailer Train Company
• STWX - Struthers Wells Corporation
• SULX - Sultran
• SUN - Sunset Railway
• SUNX - Sun Refining and Marketing Company
• SUR - State University Railroad
• SVGX - Savage services
• SVI - Southern Railway of Vancouver Island, E and N Railway
• SVIL - Saltville Railroad
• SW - Southwestern Railroad
• SWCX - Estech, Inc.
• SWFX - Southwest Forest Industries, Inc.
• SWGX - Southwest Georgia Railroad Excursion Authority/SAM Shortline Excursion Train
• SWIX - Stonewall Industries LLC
• SWLX - Essel Corporation
• SWRX - Richmond Rail Equipment Leasing Company
• SWYX - Stauffer Chemical Company of Wyoming