This is a Starship Enterprise car emblem in the style of the 'Jesus Fish', 'Darwin Walking Fish', 'Dino Eating the Jesus Fish' and 'Sci-Fi' car emblems. They cost $8 from ThinkGeek and look great on a Prius. But that's it. Don't bother buying one if you drive anything else, because it will look like shit. Plus Klingons will key your car.
Thanks to Cristen and scuttlefish, who made Millennium Falcon car emblems but George Lucas got his leak-proof Depends in a bunch about them and now they're stuck with a garage full of things they can't sell.