Section 1682. Local traffic-control devices

Local  authorities  in their
  respective jurisdiction shall place and  maintain  such  traffic-control
  devices,  conforming to the state manual and specifications, as they may
  deem necessary to indicate and carry out the provisions of this  chapter
  or  local  traffic  ordinances,  orders,  rules  or  regulations  or  to
  regulate, warn, or guide traffic, except that a city having a population
  in excess  of  one  million  shall  conform  to  the  state  manual  and
  specifications  only  insofar  as such local authority in its discretion
  deems practicable.