Both Santa Clara County and San Mateo County have rescinded the bike registration requirement that was previously in effect. This means that there is no law requiring that bicyclists register their bikes.
While there is no legal requirement, the Department of Public Safety strongly recommends that riders register their bikes, and has launched a new online bike registration program through Bike Index program. Once your bike is registered through Project Bike Index, if your bike is stolen or missing, you will be able to use the Project Bike Index system to broadcast alerts and share a photo of your bike.