We now know that a nonentity scratched his initials on one of the stones. You would think in the age of 'selfies' that carving on stones had become old hat.....

"A tour guide discovered the initials 'AA 2015' scratched into one of the stones while visiting the site.
Police Scotland and Historic Scotland have both been informed of the vandalism. It is believed it took place sometime between Monday and Thursday.
The Ring of Brodgar - the third largest stone circle in the British Isles - is regarded as one of Western Europe's most impressive prehistoric sites."

http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-33818062