In California, Special Equipment Registration is a registration program offered by the Department of Motor Vehicles (DMV) for vehicles that are not designed or used primarily for transportation on the highways.
SER is available for certain types of commercial vehicles, such as construction equipment, cranes, forklifts, or other vehicles that are used off-road or on job sites, but may occasionally be driven on public roads. SER is intended for vehicles that are not designed or used primarily for transportation on the highways, and are not used to transport property or passengers for hire.
This allows these types of vehicles to be registered with the DMV for a lower fee than a regular commercial vehicle registration, and the vehicles receive a special license plate that indicates that it is registered under the SER program.