The Federal Aviation Administration (FAA) now requires that all drone-users register (click here). The deadline is February 19, 2016, but the fee is waived if users register before January 20, 2016. Drone-users register as an operator, renewing every three years. The operator's single registration number is then used on each of their drones.
I printed out my registration number multiple times with a label maker and then stuck it on each of my drones — very easy!!! This registration is only for non-commercial drone use and there are several limitations on where and how operators fly their drones, for example they are not permitted over stadiums or within five miles of an airport.