1960-5px, 1960 U.S. National Christmas Seals, Imperforate Proof Sheet of 100 seals, pm "B", full gum, F, MNH. Firm paper, fresh, never folded, shipped flat. Scan is an example. Full scan of front and back available upon request.
Issued 1960 by the National Tuberculosis Association (NTA). Designed by Philip Richard Costigan. Four seal design of choirboys, and girls alternate in sheet. Printed by Berlin Lithography Co.
Imperforate sheets have no perforations or rouletting at all.
Christmas Seals are also known as TB Charity Seals, and are usually classified as Charity Seals, or Cinderella Stamps.