2010 New York Code
VAT - Vehicle & Traffic
Title 8 - RESPECTIVE POWERS OF STATE AND LOCAL AUTHORITIES
Article 40 - (1650 - 1652-B) REGULATION OF TRAFFIC BY COUNTY SUPERINTENDENT OF HIGHWAYS
1652-B - Supervision and installation of traffic devices in Suffolk county.

§ 1652-b. Supervision  and  installation of traffic devices in Suffolk
  county.  The county superintendent of highways of  Suffolk  county  may,
  when  authorized  by  the  Suffolk  county  governing  board,  erect and
  maintain traffic signs, signals and markings  on,  and  provide  traffic
  engineering services in relation to any highway, road or street within a
  town  or village within such county, except state highways maintained by
  the state, providing the governing body of the town  or  village  having
  jurisdiction  over  such highway, road or street determines on the basis
  of an engineering and traffic investigation  that  such  traffic  signs,
  signals  and  markings  are  necessary,  issues any necessary ordinance,
  order, rule or regulation with respect thereto, consents to the erection
  and maintenance of such traffic  signs,  signals  and  markings  by  the
  county and consents thereto by written agreement with the Suffolk county
  governing  board as to the extent of the authority and responsibility of
  the  county  superintendent  of  highways  of  Suffolk  county  and  any
  apportionment  of  costs  for  the  erection  and  maintenance of signs,
  signals and markings and traffic engineering services. The power granted
  to the Suffolk county superintendent of highways by this  section  shall
  in  no way diminish any power over roads granted to him by law but shall
  be in addition to any such powers.