| AROSC | Alfa Romeo Owners | |
| AllTimeRacing | All Time Racing | |
| AC GGC | Audi Club Golden Gate | |
| ARC | American Racing Club | |
| Cal Club | Cal Club | |
| CF | Checkered Flag | |
| CZ | Club Z | |
| DCI | Driving Concepts | |
| FL | Fast Lane | |
| GF | Green Flag | |
| HSR | Historic Sportscar Racing | |
| HOD | Hooked On Driving | |
| Lapping Days | Lapping Days | |
| NASA | NASA Pro Racing | |
| NCRC | Northern California Racing Club | |
| NCSC | Northern Cal Shelby Club | |
| OTR | Open Track Racing | |
| POCA | Pantera Owners | |
| POC | Porsche Owners Club | |
| PAS | Pro Auto Sports | |
| RF | Racer Factory | |
| RL | Redline Track Events | |
| SSCC | Silver State Classic | |
| ST USA | Speed Trial USA | |
| SV | Speed Ventures | |
| TCRA | Touring Car Club | |
| TM | Track Masters | |
| TQ | Tracquest | |
| USAS | United States Autobahn Series(Formerly MKM) |