The Agnus Dei, Cistercian art form

This side shows Mary; the other shows the Lamb of God

The Agnus Dei is not only a part of the mass often chanted, it is also a term for the small wax medallions which portray, on one side, the Easter lamb. The other side shows a given saint.
They had a special significance for the Cistercians of Santa Croce in Gerusalemme, a famous abbey in Rome, because they had been given the privilege of preparing the wax molds in a delicate and intricate process. The wax was infused with holy oil. The week after Easter, the pope would bless the Agnus Dei medallions, but not every year, only in the first and seventh years of his pontificate. They were then distributed to the faithful. A similar practice (distributing pieces of the Easter candle) was also known in the first centuries of Christendom.
Here is a video of the pope surrounded by Cistercians in 1959.

The Cistercian dimension begins in 1599, so reports Chiaravalle's homepage, when the "Foglianti" Cistercians in San Bernardo alle Terme in Rome obtained from Pope Clement VIII "an exclusive and perpetual commission" to produce the Agnus Dei. The Feuillants were disbanded in 1802 and aggregated with the Cistercian Congregation of St. Bernard in Italy, and the privilege passed to Santa Croce in Gerusalemme.