Rick,
On my car this is held on by two posts. One post is long, threaded, and has a washer & nut. The other post is short and is only there to prevent the medallion from rotating. As Bob said, look at the back side of the hood for small holes near the center of the leading edge. I think the medallions were the same through the W113 production run.
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420