Pope Francis is encouraging people to strive for joy, telling his worldwide flock, "We've never heard of a sad saint."

Some 50,000 people came to St. Peter's Square to cheer the pope during his traditional Sunday window appearance. Among them were many children clutching figurines of baby Jesus for Francis to bless for Christmas crèche scenes at home or school.

Francis said: "Man's heart desires joy. Every family, every people, aspires to happiness."

To symbolize the joy Christians experience awaiting Christmas, priests wore pink vestments at Mass Sunday. Francis said that being "missionaries of joy" should be part of lifestyles to help people face difficult situations in life.

He held up a pocket-sized prayer book and told the crowd to take free copies being distributed in the square.