Some poor bastard, fed up with his car being broken into, decided to leave this passive aggressive note for the thieves. And not only does he reference Half-Life, THE DUDE KEEPS AN OCARINA IN HIS CAR. ZOMG, do you think he's Link?! Yeah, me neither.
Also, to guy's credit, I added the asterisk to his signature. DUDE MEANS BUSINESS.
Thanks to gabby, who would have booby trapped the car with Goron bombs.