The stone stands in a flat rectangular area amidst a jumble of large recumbant stones and a cairn. The Aiggin Stone, a gritsrtone pillar, is nearly 4 feet high and has an incised cross as well as the letters I and T carved onto it. A plaque says the Aiggin Stone is a Medieval waymarker that is 600 years old. Originally it was 7 foot high but over hundreds of years it has been pushed over, or fallen over, and the lower section broken off. The stone tapers towards the top where the Latin-style cross is carved. A pointed cairn also stands here, no doubt being added to over hundreds of years by walkers traversing the ancient road between Littleborough and Ripponden high up in the Pennines.
These marker stones or waymarkers were used for religious purposes; travellers would stop at the stone and say a prayer for a safe journey over the bleak, windswept moors. Some of these stones were even used by people carrying coffins; the coffin rested here and prayers for the dead would be recited, perhaps a stone or two placed on top of the cairn as well. The letters I and T obviously have some religious significance, possibly IN TEDIUM or 'In the Lord we trust' or 'In praise of the Lord'.
There are other stones on the moors around Blackstone Edge: The Letter Stones to the south of here, the Hanging Rocks and Rocking Stone near the M62 motorway to mention but a few. Enjoy your walk.