N.Y.C. Admin. Code § 24-352: § 24-352 Execution and filing of contracts; supervision and inspection of work and materials; employer's bond.

The contracts, when so awarded, shall be executed in triplicate by the contractor or contractors on the one part and the commissioner acting for the city, on the other part. One of such originals shall be delivered to the contractor, and the other two shall be filed, one in the finance department and the other with the commissioner. The work and materials called for by such contract shall be done and furnished under the direction and supervision, and subject to the inspection of the commissioner, the commissioner's engineers, supervisors and inspectors. No contract shall take effect until the commissioner shall certify thereon in writing that the commissioner's acceptance will, in the commissioner's judgment, best secure the public interest and the efficient performance of the work therein mentioned.