California Code, Penal Code - PEN § 30960

(b)(1) Any person who registers an assault weapon during the 90-day forgiveness period described in subdivision (a), and any person whose registration form was received by the Department of Justice after January 1, 1991, and who was issued a temporary registration prior to the end of the forgiveness period, shall not be charged with a violation of subdivision (b) of former Section 12280, as added by Section 3 of Chapter 19 of the Statutes of 1989 or as subsequently amended, if law enforcement becomes aware of that violation only as a result of the registration of the assault weapon.

(2) This section shall have no effect upon any person charged prior to January 1, 1992, with a violation of subdivision (b) of former Section 12280 as added by Section 3 of Chapter 19 of the Statutes of 1989 or as subsequently amended, provided that law enforcement was aware of the violation before the weapon was registered.