What is a special sign of predestination? (Catholic)

One of the promises given by Mary to the people who pray the rosary is > Devotion to my Rosary is a special sign of predestination. Reference I read many things on predestination and can't really find a proper description of what it means in regards to this message. It's something that highlights we were predestined by God. We were predestined to receive his grace but not predestined, as Calvinists believe, to obtain his salvation after we die. Is there any explanation what it means to obtain a special sign of predestination according to the Catholic Church?