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.