Ohio Rev. Code § 735.09: Execution of contracts.

All contracts made by the director of public service shall be executed by him in the name of the city, one copy of which shall be filed in his office and one with the city auditor. No liability shall be created against the city as to any matters under the supervision of such director except by his express authority. No director of public service or officer or employee of his department shall be interested in any contract under his supervision.