It's the Feast of St. Benedict today, the founder of Western monasticism and, some would say, one of the saviors of the West itself. He died in 480 AD at the monastery of Monte Casino, the same place used as a stronghold by Nazis in WWII and subsequently destroyed at great cost.
This prayer's attributed to him, it's a form of exorcism:
Crux Sacra Sit Mihi LuxNon Draco Sit Mihi DuxVade retro SatanaNunquam suade mihi vanaSunt mala quae libas.Ipse venena bibas
Here's the initials, found on the medal itself, as an aide memoire: C S S M L – N D S M D, V R S N S M V – S M Q L I V B.
This prayer has great power. Use it.
St. Benedict, pray for us,
LSP