N.Y.C. Admin. Code § 10-309: § 10-309 Identifying marks.

a. Defacing. Any person who alters, changes, removes, disfigures, obliterates or defaces the name of the maker, model, manufacturer's or serial number of a rifle, shotgun or assault weapon shall be in violation of this section.

b. Any rifle or shotgun sold or otherwise disposed of by a licensed dealer, which does not contain a manufacturer's or serial number, must have imbedded into the metal portion of such rifle or shotgun a dealer's number. Failure to so mark and identify any rifle or shotgun shall be a violation of this section.