CAL. VEH. CODE Â 5201 .....paste
(1) The installation of a cover over a lawfully parked vehicle to
protect it from the weather and the elements does not constitute a
violation of this subdivision. A peace officer or other regularly
salaried employee of a public agency designated to enforce laws,
including local ordinances, relating to the parking of vehicles may
temporarily remove so much of the cover as is necessary to inspect
any license plate, tab, or indicia of registration on a vehicle.
(2) The installation of a license plate security cover is not a
violation of this subdivision if the device does not obstruct or
impair the recognition of the license plate information, including,
but not limited to, the issuing state, license plate number, and
registration tabs, and the cover is limited to the area directly over
the top of the registration tabs. No portion of a license plate
security cover shall rest over the license plate number.
(c) A casing, shield, frame, border, product, or other device that
obstructs or impairs the reading or recognition of a license plate
by an electronic device operated by state or local law enforcement,
an electronic device operated in connection with a toll road,
high-occupancy toll lane, toll bridge, or other toll facility, or a
remote emission sensing device, as specified in Sections 44081 and
44081.6 of the Health and Safety Code, shall not be installed on, or
affixed to, a vehicle. ....end paste.