Visited 14.6.14
I followed Chance’s directions and before too long was at the stone in question. The strange thing is it ‘felt’ like you were walking in the ‘wrong’ direction walking away from Avebury. The Avenue ‘feels’ right when walking towards the circle/henge – make of that what you will?
As stated, the marks are on the fence-side of the stone, about 1 foot above the ground.
I spotted 3 fairly deep groove lines and possibly another 3 slight grooves.
The grooves are not that obvious unless you are looking specifically for them.
Worth looking out for if walking along the Avenue.