Merchant mark of Sir Thomas Gresham, founder of the Royal Exchange, as shown on his 1544 portrait in the collection of the Mercers' Company of the City of London. Also as illustrated in Elmhirst, Edward Mars, "Merchants' Marks", ed. Dow, Leslie, Harleian Society, 1959, p.12, image no.450, shown with more pronounced "heart shape", used by other marks of this type, see for example later mark of the Honourable East India Company.