I have written before about the spiral on Stone 16. (Search for "Spiral" in the search box to find them.)
The recent Laser Scan report is silent on it except to dismiss all other "carvings" apart from the axe-heads as natural features.
But a close up of the spiral shows it is dressed in the same way as the rest of the front of 16. Was this a natural feature which had the crust removed along with the rest of the stone or was it carved by picking?
Large photos! Click for originals.
More: Original Discovery - Stone 16 Spiral