N.Y.C. Admin. Code § 6-101: § 6-101 Contracts; certificate of comptroller.

a. Any contract, except as otherwise provided in this section, shall not be binding or of any force, unless the comptroller shall indorse thereon the comptroller's certificate that there remains unexpended and unapplied a balance of the appropriation or fund applicable thereto, sufficient to pay the estimated expense of executing such contract, as certified by the officer making the same.

b. In contracts for the purchase of food supplies, forage, fuel, printing, stationery, books and other supplies required for daily or continuous use, or of supplies, materials and equipment needed for use immediately after the beginning of the next succeeding fiscal year, to be delivered within a period of one year from the date thereof, the comptroller shall indorse thereon the comptroller's certificate that there remains unexpended and unapplied a balance of the appropriation or fund applicable thereto, sufficient to pay the estimated expense of executing such contract in so far as the same is to be executed during the current fiscal year, as certified by the officer making the same. Upon the first of the following fiscal year the comptroller shall certify by indorsement upon such contract as to the portion of such contract then unexecuted, and such certification by the comptroller shall make any such contract binding and of full force.

c. It shall be the duty of the comptroller to make such indorsement upon every contract so presented to him or her, if there remains unapplied and unexpended the amount so specified by the officer making the contract, and thereafter to hold and retain such sum to pay the expense incurred until such contract shall be fully performed. Such indorsement shall be sufficient evidence of such appropriation or fund in any action.

d. The provisions of this section shall not apply to supplies, materials and equipment purchased directly by any agency pursuant to subdivisions (c) and (d) of section three hundred forty-four of the charter.