| si2 | SAS Index |
| si3 | ChessDB Index Data |
| si4 | Scid Database Index |
| si7 | SAS Index |
| siard | SIARD Database Archive |
| sic | Intuit Quicken Order Data |
| sic | Sick Submitter Data File |
| sid | Steam Game Backup Data |
| sidb | iTunes Authorization Data File |
| sidd | iTunes Authorization Data File |
| sidn | iTunes Authorization Data File |
| sie | SIE Data |
| sif | Andor SIF Data |
| sif | ElmerSolver Command File |
| sif | KilnView Log Signature |
| 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 |
| signature | e-Filing Signature Data |
| sik | Microsoft Word Backup Data |
| silo | MeshTV Data |
| sim | Simile Model |
| sim | Steam Game Backup Metadata |
| sim | CARE-S InfoWorks Simulation Parameters Data |
| simmodel | Altium Designer Simulation Model |
| simodel | Altium Designer Signal Integrity Model |
| sin | Xperia X10 Phone SIN Firmware |
| sin | WRAP SALT Input Data |
