N.Y. Veh. & Traf. Law § 1652-A
The county superintendent of highways of a county, except the county of Suffolk, having a functioning traffic engineering unit may, when authorized by the county governing board, have the responsibility and authority for the installation, removal and maintenance of traffic signs, signals and markings on, and provide traffic engineering services in relation to any highway, road or street within a city, town or village within such county, except state highways maintained by the state, providing the governing body of the city, town or village consents thereto by written agreement with the county governing board as to the extent of the authority and responsibility of the county superintendent of highways and any apportionment of costs for the installation, removal and maintenance of the signs, signals and markings and traffic engineering services. The power granted to the county superintendent of highways by this section shall in no way diminish any power over roads granted to counties or county highway superintendents but shall be in addition to any such powers.
N.Y. Veh. and Traf. Law § 1652-A