| Abbreviation | Definition |
|---|---|
| SOGS | Southwest Oklahoma Genealogical Society |
| SOIC | Society Of Inkwell Collectors |
| SOS | Save Our Scraps |
| SOSF | Soled Out San Francisco |
| SOSS | Secrets Of Speed Society |
| SOSW | SOcial SWinger |
| SOTA | Society of Typographic Aficionados |
| SOTC | State Of The Collection |
| SOTN | Socked On The Nose (stamp cancellation) |
| SOWO | Southern Worthersee |
| SPACE | Stillness, Peace, Activated Consciousness, and Exploration |
| SPAM | Septic Products As Mail |
| SPAMM | Society of Platteville Anime and Manga Maniacs |
| SPARC | Spokane Piston And Rotary Club |
| SPCA | Spark Plug Collectors Association |
| SPIRIT | Society for Paranormal Investigation Research and Informational Training |
| SPPC | Sacramento Perennial Plant Club |
| SQS | Sister's Quilt Society |
| SRL | Shadow Rangers League |
| SRL | Single Rider Line |