A person may give proof of financial responsibility by delivering to the Secretary of State a receipt of the State Treasurer showing the deposit with said State Treasurer of money in amount or securities endorsed in blank by the owner thereof and approved by said State Treasurer and of a market value in a total amount as would be required for coverage in a motor vehicle liability policy furnished by the person giving such proof under this Act. Such securities shall be of the type which may legally be purchased as investments of trust funds by trustees.