Cal. Bus. & Prof. Code § 7153

(a) It is a misdemeanor for any person to engage in the occupation of salesperson for one or more home improvement contractors within this state without having, at the time of the sales transaction, a current and valid home improvement salesperson registration issued by the registrar. If, upon investigation, the registrar has probable cause to believe that a salesperson is in violation of this section, the registrar may issue a citation pursuant to Section 7028.7.
It is a misdemeanor for any person to engage in the occupation of salesperson of home improvement goods or services within this state without having, at the time of the sales transaction, a current and valid home improvement salesperson registration issued by the registrar.
(b) Any security interest taken by a contractor, to secure any payment for the performance of any act or conduct described in Section 7151 that occurs on or after January 1, 1995, is unenforceable if the person soliciting the act or contract was not a duly registered salesperson or was not exempt from registration pursuant to Section 7152 at the time the homeowner signs the home improvement contract solicited by the salesperson.