Miraculous Medal also known as Medal of the Immaculate Conception, is a unique medal worn by millions of Catholics and even non-Catholics today. It was created by Saint Catherine Laboure upon request from Blessed Virgin Mary.
St Catherine stated that on the night of July 19, 1830, the Feast of Saint Vincent de Paul, she woke up after hearing a voice of a child calling her to the chapel, where she heard the Virgin Mary say to her
"God wishes to charge you with a mission. You will be contradicted, but do not fear; you will have the grace to do what is necessary. Tell your spiritual director all that passes within you. Times are evil in France and in the world."
On November 27, 1830, Catherine reported that the Blessed Mother returned during evening meditations. She displayed herself inside an oval frame, standing upon a globe, wearing many rings of different colours, most of which shone rays of light over the globe. Around the margin of the frame appeared the words "O Mary, conceived without sin, pray for us who have recourse to thee."
As Catherine watched, the frame seemed to rotate, showing a circle of twelve stars, a large letter M surmounted by a cross, and the stylized Sacred Heart of Jesus crowned with thorns and Sacred Heart of Mary pierced with a sword underneath. Asked why some of her rings did not shed light, Mary reportedly replied "Those are the graces for which people forget to ask."
Catherine then heard Mary ask her to take these images to her father confessor, telling him that they should be put on medallions. "All who wear them will receive great graces."
Catherine did so, and after two years' worth of investigation and observation of Catherine's normal daily behavior, the priest took the information to his archbishop without revealing Catherine's identity. The request was approved and medallions began to be produced. The blessings began to shower down on those who wore the medal, and the medal was referred as the "Miraculous Medal." They proved to be exceedingly popular and the use of the Medal spread across the whole world.
Pope John Paul II used a slight variation of the reverse image as his coat of arms, a plain cross with an M underneath the right-hand crossbar.