It's the medal of St. Benedict. Each letter stands for a latin word.
Top and bottom --> IHS (from classical greek, means Jesus) and PAX (peace)
Four letter around the cross --> (C)ross (of) (S)aint (B)enedict (P is Pater, which literally means father but stands for cristian guide)
Inside the cross --> C.S.S.M.L. Crux Santa Sit Mihi Lux (Holy cross will be my light) and N.D.S.M.D. Non Draco Sit Mihi Dux (My guide will not be the Devil)
All around it's against the devil --> V.R.S. Vade Retro Satana (Stand back Satan) N.S.M.V. Numquam Suade Mihi Vana (You don't attract me to futilities) S.M.Q.L. Sunt Mala Quae Libas (Things you offer are bad) I.V.B. Ipse Venena Bibas (drink your own poisons).
Keep in mind that St. Benedictus was born around 480 (AD of course), just 4 years after the fall of roman empire, and this cross became popular around 1050.. So it's a very old way of praying.. But it's still used and quite common in monasteries or on necklaces or bracelets..
And it's got the charm of an hold medieval stamp.. Nice wp.