To date I have yet to actually see any M-16 handguards actually stamped "Mattel". I know, there are those that swear they saw it. I will not believe it until I see it.
The original M-16's sold to the Air Force were stamped AR-15. This was before they were accepted/adopted by DoD and gained the M-designation.
In life, strive to take the high road....It offers a better field of fire.
"Robo is right" Fuzzball