Look closer to see if marked “VP” or “WD”.
From Gary Cunningham’s “bayonet points”:

Besides the V.P. CO. marked version, there is another version that is somewhat of a mystery to me. The underside of the throat has the VP/9 mark as shown earlier with the 1961 production M8A1, the body has the VP logo, but the throat is marked U.S.iconM8A1 / WD. So far I have found no record of what the WD might stand for. To complicate matters even slightly more, there are WD marked specimens that do not have either of the VP marks, and a VIZ version that is marked VIZ/WD, also with no VP marks.