| sif | Cytoscape Simple Interaction Format File |
| siff | Scene Interchange File Format Data |
| sig | Crestron Test Manager Signal Data |
| sig | Powersim Studio Simulation Game |
| sign | GNU Privacy Guard Signature Data |
| silo | MeshTV Data |
| sim | Steam Game Backup Metadata |
| sim | CARE-S InfoWorks Simulation Parameters Data |
| sim | Simile Model |
| simmodel | Altium Designer Simulation Model |
| simodel | Altium Designer Signal Integrity Model |
| sin | Xperia X10 Phone SIN Firmware |
| sip | Powersim Studio Model |
| siq | Tektronics RSA306 IQ Streaming Data |
| siqd | Tektronics RSA306 SIQ Data |
| siqh | Tektronics RSA306 SIQ Header |
| sir | Powersim Studio Simulation Run File |
| sis | Steam Game Backup Info |
| site | Sitescooper Sites Data |
| sjd | Scrapbook Factory Journal Data |
| sjf | SCAPS SAM JobFile Format |
| sk | Safari History Index |
| ska | PGP Secret Keyring Data |
| skba | Autodesk SketchBook Pro Animation File |
| skc | SideKick Card |
| skcard | Borland Sidekick Card File |
| skim | Skim Notes File |
| skindex | Apple Mail Index Data |
| skl | Autodesk Maya Skeleton Works Data |
| skn | Windows Automotive Skin |
| skr | PGP Private Keyring File |
| skr | Gaussian Scratch File |
| skypechatstyle | Skype Chat Style Data |
| skypeemoticonset | Skype Emoticon Pack |
| sl | RenderMan Shader Source |
