In the shape of a coin, religious medals are very common part of the Catholic persona and many Catholics own or often wear these items on chains around their neck. The history of practice of wearing religious medals dates back to the early days of the church.
Also known as patron saint medals, the images of Saints cut into these coins and often the words pray for us are cut into the medals forming usual the outer edge or the back. It is a common that the wearer of the patron saint medals often pick one that is in somehow are related to something they do or to someone that inspires them.
It is possible that the wearing of medals dates back into the Greek and Roman times and got carried over into the early church as a way to honor the early martyrs of the church. Exhumed bodies, as early as the 1st and 2nd centuries had the bodies wearing images of St. Paul and St. Peter embossed on a coin shaped piece of metal. These early medals have provided stories and lore of what happened to some of the martyrs in eh early days. For example St. Lawrence was believed to have been killed over an open fire. There are medals from the early first century depicting him being roasted over an open fire forming picture that tells a story.
In the early church there was many crossing overs from pagan tradition. Things like Christmas trees and advent wreaths and even saint medals, devotional medals, are believed to be having some roots into paganism mimicking the practice to wear items designed to ward off evil or disease. To reach and convert as many as possible to Christianity, the early church did reach out and allow these customs to be introduced. As they continued to evolve they became items that were used to remind folks of promised they made to others or to Christ himself. In the 1500s the custom of blessing these medals was approved by Pope Pius V. From that point forward, the agreement to bless these items was seen as an approval by the catholic church to allow these items and moved them from their pagan roots.
Usually on these coin type items the person of an famous person, event or shrine are struck to remind the wearer of these past event, miracles or dedications. They also may request personal graces like the reminder of First communion or for the priests, ordination. Medals showing events became very common as they recalled the miracles of Jesus and the apparitions of Mary
Some of the most popular medals are the Miraculous medal which was struck at the request of the blessed mother to Saint Catherine Laboure in 1830. Many now wear this medal believing it will bring them grace if they do so with piety, meaning with religious or spiritual devotion. St. Catherine is in an open glass coffin where here uncorrupted body is visible to all that go to see her.
In the 20th century its common that religious gift shops carry saint medals. But if you are looking for a wider variety of Saints or an Hard to find patron saint medal, many internet websites carry full lines of Saints and medals.