CANMORE lists this stone as a cross, and it's marked on the current OS map as a cross slab, but it was marked on the 1961 OS map as a standing stone, and visiting it seems to confirm that, it definitely looks like a christianised standing stone. So after a few second opinions I've added it here.
The stone is a large slab, 2.0m in height by 0.6m wide and 0.2m thick, giving it similar proportions to the nearby Clach Glas. On either side is carved a large simple cross.
Writing in 1925, JH Dixon described how it was supposed to have been connected with a chapel of St Maroc on the terrace above the Tay's flood plain, although no trace of such a building can now be found.