SoFo (South of Fourth Street)

"SoFo" is "South of Fourth Street" in Brooklyn. The term - a new one - is also the name of a bar there.

http://www.papermag.com/guide/bars/brooklyn.html
SOFO
550 Court St., Caroll Gardens, Brooklyn, (718) 222-3535
On the cusp of Carroll Gardens and Red Hook sits SoFo (South of Fourth Street), a cozy armchair of a bar that aspires to do nothing more than provide you with comfort beer, a game of pool and local chitchat -- the ultimate precious commodity in a neighborhood threatened by the onslaught of young professionals.

http://www.amylangfield.com/2004_06_20_archive.html
SoFo MoFo
I was walking around Court Street last weekend with the husband and Kevin of Forgotten NY when we noticed several businesses with "SoFo" in their names. Kevin, who knows an awful lot about New York, led us into SoFo dry cleaners to investigate. "South of Fourth Street" was the answer. Who knew? Court near W. 9th.