It is not decorative, not prominently displayed, and easy to pass without noticing. But the marks cut into its surface have been puzzling scholars for well over a century, and their meaning remains entirely unresolved.

The stone was first formally described by Wood-Martin in 1882, who noted its modest dimensions: roughly eighteen inches by seven, uneven in shape, set into the wall on the inner side of the entrance door. Intrigued enough to act, Wood-Martin had a cast made and sent it to Sir Samuel Ferguson, one of the foremost authorities on ogham of his day. Ogham is an early medieval Irish script, typically composed of strokes cut along the edge or angle of a stone; Ferguson concluded that this inscription was indeed ogham, but placed unusually on the flat face of the stone rather than along its edge. That interpretation did not settle the matter. By 1904, when Fennell published a sketch of the inscription, the scholarly consensus had already begun to waver. Fennell recorded that the marks had been read as ogham by some and as Roman numerals written in church text by others. Since then, neither reading has been confirmed, and no meaning has been deciphered. The inscription sits in a category of its own: not clearly one thing, not clearly another, and not yet explained.