Proof of financial responsibility may be evidenced by the bond of a surety company duly authorized to transact business within this state, or a bond with at least two individual sureties each owning real estate within this state, and together having equities equal in value to at least twice the amount of the bond, which real estate shall be scheduled in the bond approved by a judge of the superior court, which said bond shall be conditioned for payment of the amounts specified in RCW 46.29.260. Such bond shall be filed with the department and shall not be cancellable except after ten days written notice to the department.