| Signals | 529 |
| Signs | 530 |
| Signs-Maintenance & Repairing | 530 |
| Sitting Services | 531 |
| Skateboard Parks & Rinks | 531 |
| Skateboards & Equipment | 531 |
| Skating Equipment & Supplies | 531 |
| Skating Rinks | 531 |
| Skin Care | 531 |
| Slab Jacking Contractors | 531 |
| Sleep Disorders-Diagnosis & Treatment | 531 |
| Slings | 531 |
| Smoke Detectors & Alarms | 531 |
| Smokers’ Information & Treatment Centers | 531 |
| Snack Products | 531 |
| Snowball Machines | 531 |
| Snowball Machines Equipment & Supplies | 531 |
| Snowball Stands | 532 |
| Soccer Clubs & Instruction | 532 |
| Social Security Counselors & Representatives | 532 |
| Social Security Services | 532 |
| Social Service Organizations | 532 |
| Social Services Information & Referral Programs | 535 |
| Social Workers | 535 |
| Sod & Sodding Service | 536 |
| Soil Conditioners | 536 |
| Solar Energy Equipment & Systems- Dealers | 536 |
| Sound Systems & Equipment | 536 |
| Sound Systems Consultants & Designers | 536 |
| Souvenirs | 536 |
| Space Jumps | 536 |
| Space Planners | 536 |
| Spas & Hot Tubs- Service & Repair | 537 |
| Spas & Hot Tubs-Dealers | 537 |
| Spas & Hot Tubs-Supplies & Parts | 537 |
| Speech & Language Pathologists | 537 |
| Speedometers | 537 |
| Spices | 537 |
| Spill Control Equipment & Material | 537 |
| Sporting Goods | 537 |
| Sports Bars | 537 |
| Sports Cards & Memorabilia | 537 |
| Sports Clubs & Organizations | 538 |
| Sports Information | 538 |
| Sports Medicine | 543 |
| Sports Promoters, Managers & Recruiters | 543 |
| Sportswear | 543 |
| Spraying Equipment | 543 |
| Spraying-Horticultural | 543 |
| Springs-Coils, Flat, Etc-Mfrs & Distributors | 543 |
| Sprinklers-Automatic-Fire | 543 |
| Sprinklers-Garden & Lawn | 543 |
| Stables | 543 |
| Stadiums, Arenas, & Athletic Fields | 543 |
| Stages | 543 |
| Stair Builders | 544 |
| Stamps For Collectors | 544 |
| Starters-Engines | 544 |
| Starters-Engines-Mfrs | 544 |
| Steam Bath Equipment Service & Supplies | 544 |
| Steam Cleaning Equipment | 544 |
| Steamship Agencies | 544 |
| Steamship Companies | 544 |
| Steel Distributors & Warehouses | 544 |
| Steel Erectors | 544 |
| Steel Fabricators | 544 |
| Steel-Used | 545 |
| Stencils & Stencil Supplies | 545 |
| Stereophonic & High Fidelity Equipment-Dealers | 545 |