That combination, a prehistoric artefact confirmed to exist, photographed, and then lost, gives this particular record an unusual character among the ancient carved stones of the county.

Cupmarks are among the most common yet least understood forms of prehistoric rock art found across Ireland and Britain. They are shallow, roughly circular hollows pecked into stone surfaces, and while they appear throughout the landscape on exposed bedrock, boulders, and standing stones, their purpose remains a matter of ongoing debate. The stone at Milleennagun came to light not through any formal excavation but during the practical business of dismantling a field fence. When part of that boundary was removed, the marked stone was revealed beneath or within it, suggesting it had been incorporated into the wall at some earlier point, its original prehistoric context already long disturbed. According to Tony Miller, who communicated the discovery, the stone carried eight cupmarks. It was removed from that position during the clearance work, and subsequent attempts to locate it came to nothing.