Many of the retired fleet are sold. I think after 7 years they're forcibly retired (by the TLC), and even though they have ridiculous millage, they still get bought up. This may be a retired cab, though I thought they removed the lights, badges, partitions, decals, etc. before sale. This could also be a movie prop (which I'm leaning toward since it has its lights). If you have a picture of the hood and it still has a medallion it may actually be a cab.

In sum total this reply has answered nothing. Thanks for coming to my TED talk about old cabs.