Cork

"Corks" were the transit cops, who work underground and pop to the surface. There used to be transit police and housing police and the police, but Mayor Rudy Giuliani merged all three units in 1995.

Ther term "cork" - never especially popular or well-liked - is now historical.

http://www.wirednewyork.com/forum/showpost.php?p=25347&postcount=4
March 28, 2004
(From the New York Times issue on the subway centennial - ed.)
1904 - 2004
Paging Dr. Zizmor
By JACK ROSENTHAL

Corks The sarcastic nickname given to transit officers who were said to take every opportunity to rise to the surface. The nickname disappeared in 1995 when the transit and housing police were consolidated into the New York Police Department.

11 March 1986, New York Times, "The Cops and the Corks," pg. A30:
Burnt-out transit cops are called "corks," eager for any excuse to bob to the surface.

24 March 1986, New York Times, letters, pg. A18:
One more point. My members and I take offense at being called "corks." This cute turn of phrase slights the brave men and women who for more than 50 years have been dedicating - and risking - their lives to serve the people of this city. Ten have given their lives in line of duty.

WILLIAM McKECHNIE
President, N. Y. C. Transit
Patrolmen's Benevolent Association
New York, March 13, 1986