I stand corrected.
That is a Navy Commendation Medal.
While not intending to denigrate the award, in the Army the NCO medal is really not all that, that it would be put on a headstone. I should have known better.
Normally, it is the top three awards that are on the headstone, so that makes much more sense to me.
My apologies, again.
Acronyms between services are very confusing.