Nice one Rex. Technically not an M9, that's why it's not marked as such on the ricasso. This is the pattern that was submitted for the trials that Ontario won with the OKC-3S. Jim Maddox wrote an excellent article on these that first appeared in the Society of American Bayonet Collectors Journal. A copy of it can be viewed at Frank Trzaska's website.
http://www.usmilitaryknives.com/jim_maddox.htm