| sif | ElmerSolver Command File |
| sif | KilnView Log Signature |
| siff | Scene Interchange File Format Data |
| sig | Crestron Test Manager Signal Data |
| sig | Microsoft OneNote Signature Data |
| sig | Powersim Studio Simulation Game |
| sign | GNU Privacy Guard Signature Data |
| signature | e-Filing Signature Data |
| signed | BlackBerry 10 App Certificate |
| sik | Microsoft Word Backup Data |
| silk | Symbolic Link Spreadsheet |
| silo | MeshTV Data |
| silo | VisIt Hydrodynamical Numerical Simulation Data |
| sim | CARE-S InfoWorks Simulation Parameters Data |
| sim | ESI ITI SimulationX Model |
| sim | Intel VTune Performance Monitor Simulation Data |
| sim | Simile Model |
| sim | Stagecast Creator Simulation Data |
| sim | Steam Game Backup Metadata |
| simfreq | PLINK Simulation Parameter Data |
| simmodel | Altium Designer Simulation Model |
| simodel | Altium Designer Signal Integrity Model |
| sin | WRAP SALT Input Data |
| 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 | arivis ImageCore Data |
