The mark has been attributed in the past to James Harris of Dundee, but I've always had a sneaking feeling that we are not supposed to know the actual maker. Similar marking has been noted by 'D' with three pots of lillies, and 'W' with three pots of lillies, and I think that such marking was applied following pressure by the Edinburgh Assay Office to make Dundee silversmiths comply with the hallmarking laws of the period, threatening them with large fines for non-compliance. The striking of the single letter would no doubt make it harder for the authorities to successfully prove the identity of the manufacturer.