Yes. A summons is an order to appear and your signature is a "promise to appear."
You have two options:
- Sign the ticket and go on your way
- Don’t sign and go to jail for refusing to promise to appear. California Vehicle Code 40302 section (b) states: Whenever any person is arrested for any violation of this code, not declared to be a felony, the arrested person shall be taken without unnecessary delay before a magistrate within the county in which the offense charged is alleged to have been committed and who has jurisdiction of the offense and is nearest or most accessible with reference to the place where the arrest is made.