Way back in 2008, the California Air Resources Board (CARB) decided to make it illegal to idle diesel-engined trucks with a gross vehicle weight rating (GVWR) over 14,000 pounds for more than five minutes. That GVWR is above that of most heavy-duty pickups like the Dodge Ram 3500, Ford F-350 and GMC Sierra 3500, but does cover most chassis-cab trucks.
CARB's regulation says that manufacturers of diesel engines have to either incorporate an anti-idling system or to certify that the engine emits 30 grams or fewer of nitrogen oxide per hour in order to get a sticker. If the oil-burning engine meets that limit, it can, at least in theory, idle forever.
For 2011, the Ram 4500/5500 and Ford F-450/F-550 chassis-cab trucks meet CARB's certified clean idle requirements, meaning that they get one them flashy stickers (pictured). Being able to idle indefinitely isn't really sticker-worthy, right?
[Source: Pickup Trucks via Autoguide]