| 5001 | SIMW | SIMKINS TRUCKING CO | | | SCAC4 |
| 5002 | SIMX | Simms Oil Co. | 7/1930-7/1935 | | NAKINA |
| 5003 | SIMX | Shippers Car Line Corp. | 7/1937 | | NAKINA |
| 5004 | SIMX | North American Car Corp. | added 7/1964; 7/1965-4/1970; eliminated 7/1972 | | NAKINA |
| 5005 | SIMX | Sierra Bag Co. | added 1/1983; eliminated 1/1989 | | NAKINA |
| 5006 | SIMX | Sturgis Iron & Metal Co., Inc. | 7/2005 (not listed) | | NAKINA |
| 5007 | SIMX | Ominsource Corp. | added 1/2009 | | NAKINA |
| 5008 | SIMX | North American Car Corp. | added 7/64; 7/65-4/70 | | NRHS |
| 5009 | SIMX | Sierra Bag Co. | added 1/83; eliminated 1/89 | | NRHS |
| 5010 | SIMX | *SIMMS OIL CO. (SHIPPER' CAR LINE CORP.) | | | PWRC |
| 5011 | SIMX | *NORTH AMERICAN CAR CORP. | | | PWRC |
| 5012 | SIMX | *SIERRA BAG CO. | | | PWRC |
| 5013 | SIMX | +STURGIS IRON & METAL CO., INC. | | | PWRC |
| 5014 | SIMX | Sierra Bag | | | RSRV |
| 5015 | SIMX | STURGIS IRON & METAL CO INC | | | SCAC4 |
| 5016 | SIMZ | SIMPLOT | | | PWRC |
| 5017 | SIN | Sinair | Callsign: Sinairline, | F | AVCODES |
| 5018 | SIN | Servizi Aerei Industriali S.p.A. | Callsign: Infrarosso, | I | AVCODES |
| 5019 | SIN | Santair | Callsign: Santair, | GR | AVCODES |
| 5020 | SINA | SINCLAIR MOVING & STORAGE INC | | | SCAC4 |
| 5021 | SINB | SINOTRANS (BERMUDA) LTD | | | SCAC4 |
| 5022 | SIND | Southern Indiana Ry., Inc. | 1/1975-1/1980; eliminated 7/1989; 1/1994-7/2005 | | NAKINA |
| 5023 | SIND | Southern Indiana Ry., Inc. | 1/75-1/80; eliminated 7/89; 1/94-7/2000 | | NRHS |
| 5024 | SIND | SOUTHERN INDIANA RAILWAY, INC. | | | PWRC |
| 5025 | SIND | Southern Indiana Railway | | | RSRV |
| 5026 | SINF | SIMARD, N & FRERES INC | | | SCAC4 |
| 5027 | SINH | SOUTHERN INDUSTRIAL & TRUCK LTD | | | SCAC4 |
| 5028 | SINK | SCISENSE INC | | | SCAC4 |
| 5029 | SINL | STRITE INDUSTRIES LIMITED | | | SCAC4 |
| 5030 | SINM | SUPERION INC | | | SCAC4 |
| 5031 | SINN | SINGER TRANSPORT INC | | | SCAC4 |
| 5032 | SINO | SINO-AMERICAN CORP | | | SCAC1 |
| 5033 | SINO | SINO CONNECTIONS LOGISTICS LTD | | | SCAC4 |
| 5034 | SINP | STIM INTERNATIONAL INC | | | SCAC4 |
| 5035 | SINQ | SCAFFS INCORPORATED | | | SCAC4 |
| 5036 | SINS | SINDEN RACING SERVICE INC | | | SCAC4 |
| 5037 | SINT | SUNTRUCK INC | | | SCAC4 |
| 5038 | SINTR | SERVICIOS INDUSTRIALES Y TRANSPORTES, S.A. | | ES | VKM |
| 5039 | SINU | BBC CHARTERING GMBH & CO. KG | | D | BIC |
| 5040 | SINV | SINCERE NAVIGATION CORPORATION | | | SCAC4 |
| 5041 | SINW | SHIP NOW INC | | | SCAC4 |
| 5042 | SINZ | SAUDER INDUSTRIES | | | PWRC |
| 5043 | SINZR | ŠINVOZ A.D., Zrenjanin | | RS | VKM |
| 5044 | SIO | Sirio S.p.A. | Callsign: Sirio, | I | AVCODES |
| 5045 | SIO | Sirio | | | ICAO1 |
| 5046 | SIO | Siófok | City: Siófok | H | TRAFFIC |
| 5047 | SIOA | SIORDIA MADRIGAL, LUIS ARMANDO | | | SCAC4 |
| 5048 | SIOC | SSI OCEAN SERVICES INC | | | SCAC4 |
| 5049 | SIOE | SIO, KEN S SEAFOOD | | | SCAC4 |
| 5050 | SIOF | SCHRADER OIL CO | | | SCAC4 |
| 5051 | SIOH | SINCLAIRE OIL & HEATING | | | SCAC4 |
| 5052 | SIOK | SIMONS TRUCKING INC | | | SCAC4 |
| 5053 | SIOL | SISSEL ONLINE LTD | | | SCAC4 |
| 5054 | SION | SAGOVI CRUCES INTERNACIONALES | | | SCAC4 |
| 5055 | SIOR | SUPERIOR BURNER SERVICE INC | | | SCAC4 |
| 5056 | SIOS | S L I OF USA INC | | | SCAC4 |
| 5057 | SIOT | SION TRANSPORT INC | | | SCAC4 |
| 5058 | SIOU | AROS LINE AB | | | SCAC3 |
| 5059 | SIOUX | Sioux City Transit | Real: SCT, City: Sioux City, IA | USA | TRAFFIC |
| 5060 | SIOY | SHIPLEY OIL COMPANY | | | SCAC4 |
| 5061 | SIP | Air Spirit, Inc. | Callsign: Air Spirit, | USA | AVCODES |
| 5062 | SIP | Air Spirit | | | ICAO1 |
| 5063 | SIPF | SIMPLIFIED EXPRESS INC | | | SCAC4 |
| 5064 | SIPG | SHIP DTS | | | SCAC4 |
| 5065 | SIPJ | STAR INTERMODAL TRANSPORTATION INC | | | SCAC4 |
| 5066 | SIPL | SMITH TRANSPORTATION LLC | | | SCAC4 |
| 5067 | SIPM | SIMONS PETROLEUM INC | | | SCAC4 |
| 5068 | SIPO | SISIPO TRANSPORTS S DE R L DE C V | | | SCAC4 |
| 5069 | SIPP | SIPPIN ENERGY PRODUCTS | | | SCAC4 |
| 5070 | SIPPEL | Sippel GmbH | | D | TRAFFIC |
| 5071 | SIPR | STRONG INTERNATIONAL CORPORATION | | | SCAC4 |
| 5072 | SIPT | SIPPS TRUCKING | | | SCAC4 |
| 5073 | SIPU | PT PERUSAHAAN PELAYARAN NUSANTARA PANURJWAN | | RI | BIC |
| 5074 | SIPX | Arrendadora Sipco, S.A. de C.V. | added 7/1994; 7/2000-7/2005 (not listed) | | NAKINA |
| 5075 | SIPX | Arrendadora Sipco, S.A. de C.V. | added 7/94; 7/2000 | | NRHS |
| 5076 | SIPX | ARRENDADORA SIPCO SA DE CV | | | PWRC |
| 5077 | SIPX | Arrendadora Sipco | | | RSRV |
| 5078 | SIPX | ARRENDADORA SIPCO, S.A. DE C.V. | | | SCAC4 |
| 5079 | SIPZ | SIMPSON PAPER | | | PWRC |
| 5080 | SIQ | National Center for Atmospheric Research | Callsign: Science Quest, Name changed to Atmospheric Research Boulder. | USA | AVCODES |
| 5081 | SIQ | Simon Air | IATA: 8U, Callsign: Simon, Designator 8U recalled by IATA | LB | AVCODES |
| 5082 | SIQ | Atmospheric Research Boulder | Callsign: Science Quest, Name changed from National Center for Atmospheric Research. | USA | AVCODES |
| 5083 | SIQA | SINO AMERICAN LINE | | | SCAC4 |
| 5084 | SIQG | SINGLE SOURCE LOGISTICS INC | | | SCAC4 |
| 5085 | SIQM | SEAPORT INTERMODAL | | | SCAC4 |
| 5086 | SIQN | SONEIL INTERNATIONAL LIMITED | | | SCAC4 |
| 5087 | SIR | Salair, Inc. | Callsign: Salair, IATA designator 8S recalled by IATA | USA | AVCODES |
| 5088 | SIR | Salair, Inc. | IATA: 8S, Callsign: Salair, IATA designator 8S recalled by IATA. IATA designator 8S reinstated by IATA | USA | AVCODES |
| 5089 | SIR | Salair | | | ICAO1 |
| 5090 | SIR | Staten Island Rapid Transit Ry., Co. | 8/1920-4/1970 | | NAKINA |
| 5091 | SIR | Staten Island Rapid Transit Ry., Co. | 4/38-4/70 | | NRHS |
| 5092 | SIR | B&O [STATEN ISLAND RAPID TRANSIT RY] | | | PWRC |
| 5093 | SIRC | Staten Island R.R. Corp. | 1/1975-1/1980; eliminated 7/1985 (see SIRY) | | NAKINA |
| 5094 | SIRC | Staten Island R.R. Corp. | 1/75-1/80 | | NRHS |
| 5095 | SIRC | STATEN ISLAND RAILROAD | | | PWRC |
| 5096 | SIRC | Staten Island Railroad | | | RSRV |
| 5097 | SIRE | SIR LANCELLOT COURIER AND DELIVERY | | | SCAC4 |
| 5098 | SIRH | SINGH, ROHINI | | | SCAC4 |
| 5099 | SIRI | SRC IRRIGATION INC | | | SCAC4 |
| 5100 | SIRP | SHIPPING INTERESTS | | | SCAC4 |
