If you’re flying any of the following; Fixed Wing aircraft, Helicopter, and or Multi-Rotor (AKA Drone), you must register with the FAA and receive a UAS certificate number.
See the FAA.gov/uas/registration page for registration and rules on carrying and displaying the certificate/number.
“Effective December 21, 2015, anyone who owns a small unmanned aircraft of a certain weight must register with the Federal Aviation Administration’s Unmanned Aircraft System (UAS) registry before they fly outdoors. People who previously operated their UAS must register by February 19, 2016. People who do not register could face civil and criminal penalties.”
see the following links for detailed information.