This standing stone has been inscribed with the Ogam writing system as well as Latin. Ogam consisted of horizontal and diagonal lines, and was developed in Ireland in the AD300s. It can be seen around the edges on this stone, and was apparently used for dedications and memorials.
I’ve no idea how anyone could read it, but I daresay that if an Irish person from AD300 found themselves transported to 21st century Ireland, they wouldn’t understand it either.
I was a bit disappointed that Ogam does not appear to be mentioned in The Written World, at least not according to the table of contents or the index. Well, I don’t suppose everything could be covered. It would be interesting to find out more about this methinks.