King James I granted Penzance The Charter on 16th May 1614
The Seal was Adopted 9th october 1620
When devising the seal, it is reported that no-one truly knew what Pen Sans meant and assumed that it was holy head, rather than holy headland, and so took the visual pun of St John's Head on a Platter. I am sure that they were more astute than that for which they are given credit.
Instead, this is a direct reference to the times in Madron of The Knights Hospitallers of S. John of Jerusalem.
This marble medallion was sculpted by the mason Mr Isabell of Truro in 1803 and was later removed from the original Market House to be placed her on the new Market House. It was written of by Valentine Le Grice in the Royal Cornwall Gazette in 1803, it therefore follows that it had to have been made and positioned before that date.