N.Y.C. Admin. Code § 27-2053: § 27-2053 Obligations of owner.

a. The owner of a multiple dwelling shall provide adequate janitorial services.

b. In a multiple dwelling of nine or more dwelling units, the owner shall either:

(1) Perform the janitorial services himself or herself, if he or she is a resident owner; or

(2) Provide a janitor; or

(3) Provide for janitorial services to be performed on a twenty-four-hour-a-day basis in a manner approved by the department.

c. The owner of a multiple dwelling or his or her managing agent in control shall post and maintain in such dwelling a legible sign, conspicuously displayed, containing the janitor's name, address (including apartment number) and telephone number. A new identification sign shall be posted and maintained within five days following a change of janitor.