In October, the FAA clarified that aircraft registration requirements do apply to drones (UAS) and stated that most versions of even small, recreational drones will be required to be registered for safety and accountability. As currently recommended, drones weighing as little as 250 grams, or about 9 ounces, will fall under the requirement. More here from the Aircraft Owners and Pilots Association, which participated on the FAA recommendation committee:
Miami is considering legislation that would restrict the use of drones over large gatherings, festivals, and stadiums.
(c) Cameron Davidson 2015