Mr Looney (of Looney-Field-Effect notoriety!) informs me that this is 'the grocer's apostrophe' and causes much merriment. It certainly gave me a chuckle as I went walking around Ballsbridge this morning. The Wikipedia, of course, has an article that describes the (green)grocer's apostrophe's phenomenon.
It has been a while since I belly-ached about apostrophes and quotation marks.