It's an Arizona thing.. all you need is a headlight, tail light, 1 mirror and a horn and you are "street legal". If you're riding in the city you may get hassled for not having DOT tires but otherwise it's game on.
Actually there's no such thing as "DOT" law or regs for motorcycle tires, unless of course you are hauling freight for hire and stop at all ports and pay road use taxes.
Yes... it don't take much to plate a bike here in AZ. The headlight and tail light don't work and are only on there for fooling the PoPo whenever I ride from my house to the trails. Most PoPo around here won't even blink if they see a head light on what looks like a streetable bike, but boy if they see number plates, your ass is theirs.