N.Y.C. Admin. Code § 14-110: § 14-110 Warrant of appointment; oath.

a. Every member of the force shall have issued to him or her by the department, a proper warrant of appointment, signed by the commissioner and chief clerk or first deputy clerk of the department or of the commissioner, which warrant shall contain the date of appointment and rank.

b. Each member of the force shall, before entering upon the duties of his or her office, take an oath of office and subscribe the same before any officer of the department who is empowered to administer an oath.