It is roughly L-shaped, no more than two metres at its longest, and weathered to the point where moss has colonised much of its surface. What makes it quietly extraordinary is what has been carved into it: a carefully composed arrangement of prehistoric markings covering both its east and west faces, partly swallowed now by accumulated soil and creeping sod.

The carvings belong to the tradition of Atlantic rock art, a form of abstract prehistoric decoration found across Ireland, Britain, and the Atlantic fringe of Europe, generally dated to the Neolithic and early Bronze Age. The vocabulary is limited but precise: cupmarks, which are small hemispherical hollows pecked into the stone surface; cup-and-ring motifs, where one or more concentric rings are carved around a central cup; and grooves connecting or radiating from these forms. At Ballynahow Beg, the east-facing surface, the more densely decorated of the two, groups several of these motifs together and encloses them within a grid of intersecting linear grooves, an unusual structural element that gives the composition a more deliberate, almost diagrammatic quality. One cup-and-two-ring motif has its own radial groove extending outward from the cup to the edge of the outer ring. Elsewhere on the same face, six small cupmarks are arranged in a cluster to form what is described as a rosette motif, roughly eight centimetres across. The west-facing surface carries a single large cupmark with a linear groove running from it. Some connections recorded between motifs in earlier documentation are no longer visible, buried beneath soil that has quietly risen around the stone over the intervening decades.

The site sits toward the base of a north-facing slope at around forty metres above sea level, with a hedgerow field boundary close to the north that limits the view in that direction. Because soil continues to accumulate along the eastern side of the outcrop, some of the lower motifs on the east face are no longer accessible to the eye, making earlier drawn records particularly valuable for understanding the full extent of the carving programme. Visitors approaching the stone should look carefully across the surface at a low angle, especially in raking light, which tends to bring shallow carved forms into sharper relief against the surrounding rock.