When a mortgage or deed of trust is executed as security for money due or to become due, on a promissory note, bond, or other instrument, designated in the mortgage or deed of trust, the record of the assignment of the mortgage or of the assignment of the beneficial interest under the deed of trust, is not of itself notice to the debtor, his heirs, or personal representatives, so as to invalidate any payment made by them, or any of them, to the person holding such note, bond, or other instrument.