What GodSilla said. It's part of the laws that say bikes must have turn signals, a horn, sidestand interlocks, etc. The Federal Saftey sticker that goes on the bike next to the emissions sticker is certifying that the bike meets all these fed standards. There are a lot of them, but there are a lot less for bikes than there are for cars. The federal law only covers the equipment. It's up to the states to decide if you have to use it. OR requires bikes to have their headlights on at all times, IIRC CA doesn't.