The hypothecation of the securities referred to in section 131.13 of the Revised Code shall be the proper legal transfer thereof as collateral which shall stipulate that such securities shall be the property of the depositor in case of any default on the part of the bank in its capacity as depository, and the negotiation or release thereof shall require the signature of the depositor except when the securities have been deposited with a trustee for safekeeping and eligible securities are substituted therefor as provided in section 131.15 of the Revised Code.