These rings are inscribed with the word "FAITH" in Ogham (pronounced "Oh-um"), the earliest form of written language in Ireland. The ogham alphet consists of lines etched into stone or drawn on parchment. Ogham is generally written vertically from the base of the stone to the top, using the edge of the stone as a central axis.
There is much speculation that ogham was carved into tree trunks. Indeed, many of the letters are named after native Irish tree species. However, the only surviving ogham inscriptions we have today are on parchment and standing stones (such as the example in the picture above). There are upwards of 180 ogham stones standing in the south and west of Ireland with the earliest surviving examples dating from the 4th century. The vast majority of inscriptions honor the names of important individuals.