This, writes Gawker's John Cook, is a taxi used in "NYPD's indiscriminate and probably illegal spying program." According to the two Pulitzer Prize–winning authors of the book, Enemies Within, it's a "real yellow cab, complete with an authentic taxi medallion registered under a fake name used by the department's intelligence division to conduct surveillance operations."
It's mainly used to keep tabs on activities around New York's mosques, say the book's authors, Matt Apuzzo and Adam Goldman.
Cook's advice, "If you hail this cab, don't tip."