Here is the document in which St Pius X introduced the Scapular Medal:
Holy Office December 16, 1910
For the future all the faithful already inscribed or who shall be inscribed in one or other of the real Scapulars approved by the Holy See (excepting those which are proper to the Third Orders) by what is known as regular enrollment may, instead of the cloth scapulars, one or several, wear on their persons, either round the neck or otherwise, provided it be in a becoming manner, a single medal of metal, through which, by the observance of laws laid down for each scapular, they shall be enabled to share in and gain all the spiritual favors (not excepting what is known as the Sabbatine Privilege of the Scapular of Our Lady of Mount Carmel), and all the privileges attached to each.
The right side of this medal must show the image of Our Most Holy Redeemer, Jesus Christ, showing His Sacred Heart, and the obverse that of the Most Blessed Virgin Mary. It must be blessed with a separate blessing for each of the scapulars in which the person has been enrolled and for which the wearer wishes it to suffice. Finally, these separate blessings may be given by a single sign of the cross (unico crucis signo), whether in the act of enrollment or later at the convenience of those enrolled, it matters not how long after the enrollment or in what order they may have taken place; the blessing may be given by a priest other than the one who made the enrollment, as long as he possesses the faculty, ordinary, or delegated, of blessing the different scapulars- the limitations, clauses, and conditions attached to the faculty he uses still holding their force. All things to the contrary, even those calling for special mention, notwithstanding"
Holy Office, Rome, December 16, 1910
Here are some lovely examples of Scapulars that you can find in my shop: