The words "Con clavi con dio" roughly translates into "With nails, with God."
This saying is mainly popular with fans of the band Ghost which records and performs pop hymns that glorify and glamorise the disgusting and sacrilegious (according to their Facebook page).
They have a song titled "Con Clavi Con Dio", the first track on their debut record, Opus Eponymous, is supposedly an evil song about Satan.
See annotations and interpretation of the lyrics of "Con Clavi Con Dio" on Genius.com.
For news and updates on Ghost's song and albums releases and upcoming tours, follow them on Twitter and visit their website at ghost-official.com.