Originally Posted by Appowner

Don't know what document you were looking at but since it cites both the FAA # and the AMA #, it was no doubt an AMA declaration. Legally all you need is the FAA# and it comes from the FAA and the FARs. Legibly on the outside of the model somewhere. I use a small font and stick mine on the fuselage side under the stab.

AMA # is something dictated by the AMA. I have yet to see it enforced for anything other than a contest. Most clubs don't want to get into policing for numbers.