You can read about devotional scapulars here. Readers may be aware the etymology of the word, derived from “shoulder” in Latin. The full scapular is a monastic garment worn over the upper torso. For laity, it is something like a badge.
205. The history of Marian piety also includes “devotion” to various scapulars, the most common of which is devotion to the Scapular of Our Lady of Mount Carmel. Its use is truly universal and, undoubtedly, its is one of those pious practices which the Council described as “recommended by the Magisterium throughout the centuries” (Lumen Gentium 67; cf. Paul VI Letter to Cardinal Silva Henriquez, Papal Legate to the Marian Congress in Santo Domingo, in AAS 57 (1965) 376-379).
The Scapular of Mount Carmel is a reduced form of the religious habit of the Order of the Friars of the Blessed Virgin of Mount Carmel. Its use is very diffuse and often independent of the life and spirituality of the Carmelite family.
Derived from something of religious life, but in its physical form, something of a minimalist expression.
The Scapular is an external sign of the filial relationship established between the Blessed Virgin Mary, Mother and Queen of Mount Carmel, and the faithful who entrust themselves totally to her protection, who have recourse to her maternal intercession, who are mindful of the primacy of the spiritual life and the need for prayer.
Take the scapular seriously, we are cautioned:
The Scapular is imposed by a special rite of the Church which describes it as ” a reminder that in Baptism we have been clothed in Christ, with the assistance of the Blessed Virgin Mary, solicitous for our conformation to the Word Incarnate, to the praise of the Trinity, we may come to our heavenly home wearing our nuptial garb” (CDWDS, Circular Letter Guidelines and proposals for the celebration of the Marian Year,88).
The imposition of the Scapular should be celebrated with “the seriousness of its origins. It should not be improvised. The Scapular should be imposed following a period of preparation during which the faithful are made aware of the nature and ends of the association they are about to join and of the obligations they assume” (Book of Blessings 1213).
When I was a boy, I was given two scapulars as gifts on two different occasions. No explanation from the givers. I wonder how many serve as just spiritual keepsakes.
The Directory on Popular Piety and the Liturgy is online at the Vatican site.