As long as no signs are posted one can make a u-turn in a residential neighborhood. In a business district it is illegal even without a sign.
From the NYS Driver’s Manual Page 50:
You may not make a U-turn near
the crest of a hill, a curve or any other
place where other drivers cannot see your vehicle from 500 feet (150 m) away in
either direction. U-turns are also illegal in business districts of New York City and
where NO U-TURN signs are posted. You may never make a U-turn on a limited
access expressway, even if paths connect your side of the expressway with the
other side.