Police Taxi:

Two key factors are accomplished with this police car

1. The element of surprise
2. Bragging rights for the coolest idea in police tactics

Seriously though, they could be more secretive about it. The NYPD views the police as more effective as a noticeable presence, rather than undercover. I am sure they have multiple levels of undercover officers, and this car with multiple sirens and the casual pullovers and busts that vehicles of this type pull is on the low end of 'undercover.'

elmblog wants to know what makes it noticeable as a police vehicle. And I guess that's important information so:

• The license plate is 8 consecutive digits, usually beginning with 'T8OO", while most civilian plates for New York State are 7 digits with a space between the first three digits and the last four, and more importantly most taxicabs in New York City have only four digits on their plates which match the medallion number on the roof light.
• On the trunk lid, there is an extra black thing protruding about 4 inches. This is a police radio antenna or something like it. 
• The black trim on the side doors, door in this case, is rarely ever on a real New York City cab anymore.

Other features on the police car that are not shown in this picture:

• There is no partition, and while there are a few taxis without partitions, the front seats are made of cloth rather than the leather like material mandated by the taxi commission.
• Sometimes an on board shockproof laptop computer is mounted between the two front seats.
• The Police-cabs are often driven in groups of three very police looking people.
• And the most obvious reason, is sometimes that the car is parked on the same block as the police precinct and the bulb siren is sitting on the dashboard.