I'm tempted to post an image of what quarrymen's marks really look like.
I've posted it before.
Ditto again. The thing above the circle at Greelee Lough. Remember that? Points out that people have been making those marks for more than a couple of hundred years, but they were still quarry marks. At Greenlee they are probably roman quarry marks.
It also links in to the other question:
'if they went to all that trouble to mark the stone why did they then abandon it' ?
In the case of the one at Greenlee, I reckon the answer is because someone prevented further quarrying. But I don't have any evidence, so I won't bang on endlessly about it. There are others, quarried more recently, such as the ones at Lordenshaw, Roughting Linn, Old Bewick, Chatton Camp etc, where there is evidence that quarrying was halted once the ancient nature of the stones was recognised.