i've lived in NY for the past 22 yrs (til recently) and i've only seen a handful of them. HLF, corner strobes, pair of red grill cudas, a FS beacon on the dash, strobes on the reverse lights. i've only seen them with uniformed officers operating w/ them, though, and with the exception of one time (when it was at a minor prop.-damage MVA 2 blocks away from the local task force HQ/precinct), i personally've only seen those unmarked NYPD taxis pulling ppl over/on V&T's, never responding Code3 across town to calls.
(it was kinda funny tho....on the one time when i saw the officers w/ the undercover taxi at the MVA, a snotty lady came up and started yelling at the officer, who was trying to collect info from the drivers involved in the MVA, to get back in the cab and take her to wherever....even w/ the uniformed officers, flashing lights on the vehicle, laptop in the center, and she still thought it was a cab waiting for her for a fare? :lol: common sense is so uncommon.)