Six Weeks in the Scottish Highlands (London: Burton, 1837), Chauncy Garms's account of travels in the Kilmartin Valley of Scotland in 1835, includes a tale of a family burial site near Loch Fearphorm. Garms notes that certain stones there bore looped marks (above left) similar to the Mesopotamean symbol (above right) that Johnson sites as antecedent to the former Greens' logo, the ancient Roman uncial g. Garms offers the following drawing of the five Fearphorm stones which bear this symbol, arranged, not in a quincunx pattern, but in a pentagon, thus:
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Subsequent archeological investigations in the Kilmartin Valley have not located any evidence of this site, despite two major excavations, Sven Troad (1923) and Alice Claire James (1987). Garms fails to specify the location of the site exactly (perhaps as much for fear of vandals as for his status as tourist), though the book's other references to known archeologial sites in the valley legitimate his claims.
Hadrian's Wall is, of course, a good deal south of this site, so there's some question as to the legitimacy of Roman borrowing or influence. More likely, the stones, if they do exist, demonstrate a family crest of some kind. We can only speculate about the grounds for their pentagonal arrangement. Conclusions such as these open a wide field for speculation and exciting conjecture.