This isn't my car. I don't drive a Mercedes. I drive a Subaru. It's hard to tell, but I don't think that's even a California license plate.
For the curious, "kos" also means "cunt" in Farsi, and is a Greek island in the Aegean Sea. Both good reasons for someone to stick "kos" on a license plate.
Finally, I think personalized license plates are cheesy. You wouldn't catch me dead with one of those.
Update: Per the comments, "kos" also means the Jugoslav secret police, "kill on sight" in gamer's parlance, and "blackbird" in Serbian. Oh, and in India, it's a "variable measure of distance, usually estimated at two miles."