Catherine Labouré stated that on 18 July 1830, the eve of the feast of Saint Vincent de Paul, she woke up after hearing the 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 27 November 1830 Catherine reported that the Blessed Mother returned during evening meditations. She displayed herself inside an oval frame, standing upon a globe. She wore many rings set with gems that shone rays of light over the globe. Around the margin of the frame appeared the words Ô Marie, conçue sans péché, priez pour nous qui avons recours à vous ("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 Immaculate Heart of Mary pierced with a sword. Asked why some of the gems did not shed light, Mary reportedly replied, "Those are the graces for which people forget to ask." Sister Catherine then heard the Virgin Mary ask her to take these images to her father confessor, telling him that they should be put on medallions, and saying "All who wear them will receive great graces."
Source:  Wikipedia



Symbolism

The elements of the design encapsulate major Marian tenets and of the Catholic faith.

Front side:

• Mother – Her open arms, the "recourse" we have in her.
• Immaculate – The words, "conceived without sin."
• Assumed into Heaven – She stands on the globe.
• Mediatrix – Rays from her hands symbolizing "graces."
• Our Protection – Crushes the serpent (Gn 3:15).

Reverse side:

• The large letter "M" – Mary as Mother, Mediatrix.
• Cross and bar – Jesus' Cross of Redemption. Interleaving of the M and the cross shows Mary’s close involvement with Jesus, which also implied her role as mediatrix
• 12 stars – 12 Apostles; also recall the vision of Saint John as experienced in Book of Revelation 12:1: "And a great sign appeared in heaven: A woman clothed with the sun, and the moon under her feet, and on her head a crown of twelve stars"
• Left Heart – The Sacred Heart of Jesus, who died for the sins of humankind.
• Right Heart – The Immaculate Heart of Mary, who intercedes for sinners.
• Flames around both hearts – The burning love Jesus and Mary have for all people.

Source:  Wikipedia

Prayer to Our Lady of the Miraculous Medal

Good and kind Lady, we bring to You our petitions and intentions. Listen to us in our dire necessities. You have promised that whoever wears this medal will receive great graces. Most Blessed Mother, we ask for a miracle. Please entreat God by your persistence and tact to hear our desperate prayers. (Mention them).

O Mary, who was conceived without sin, pray for us who have recourse to thee!

O Mary, who was conceived without sin, pray for us who have recourse to thee!

O Mary, who was conceived without sin, pray for us who have recourse to thee!

Amen.