It is against the public policy of this state to allow one spouse to obligate community property by entering into a contract of indemnity whereby he will indemnify a surety company in case of default of the principal upon a bond or undertaking issued in consideration of the contract of indemnity. No community property shall be liable for any indebtedness incurred as a result of any contract of indemnity made after the effective date of this section, unless both husband and wife sign the contract of indemnity.