If you have a California drivers license, itu2019s a rebuttable presumption that your out of state vehicle is actually domiciled in California and you are a in fact a resident. Law sectionIf you drive a vehicle in California more than in other states, even if you arenu2019t a resident, you have to register it. Law sectionThereu2019s a whole section regarding people who live out of state but work in California, who needs commuter passes and when registration is required. If you move to California, you have 20 days to register the vehicle, and only 10 days to get a new license.Your friends can also rat you out: Cheaters: Out-of-State (Out of State Registration Violators)So, when stopped by the police you can get a registration ticket which would cause you to get the vehicle registered to dismiss the ticket.We used to have a form which would get sent to the State Board of Equalization (sales tax) which would put you in their sights, and they would assess you for u2018Use Taxu2019, which oddly enough was the same rate as the sales tax.You donu2019t have to register your private fire engine if you use it only for fighting fires, though.