Perkins, Fairman, & Heath, a proof for an advertising note denominated £1, circa 1820, displaying their new ‘Siderographic’ method with several vignettes and the text “Specimen of the plan for preventing the forgery of bank notes submitted to the bankers or the United Kingdom by Perkins, Fairman & Heath, 69 Fleet Street, London”, reverse entirely blue, about uncirculated, scarce £150-£200