As of May 2017, information on this page is in the process of changing. The FAA registration requirement is likely to be obsolete, having been struck down by the courts, thanks to an attorney and AMA member.
The FAA registration is a requirement for all people flying model aircraft. According with the FAA guidelines, members need to list both the AMA number and the Federal registration number on their aircraft, at least until a new registration process is finalized with the FAA.
For FAA registration, the official website is at: https://registermyuas.faa.gov/
Questions and Answers on the UAS registration can be found on the FAA website, at: https://www.faa.gov/uas/registration/faqs/
The AMA position on the registration process is summarized at: http://amablog.modelaircraft.org/amagov/2016/01/11/update-uas-registration-frequently-asked-questions/
Also read the AMA message released on July 21, 2016, about the latest FAA position on aero modeling, by clicking here.