1951-1px, 1951 U.S. National Christmas Seals, Imperforate Proof Sheet of 100 seals, pm "E", F, No Gum. Firm paper, fresh, never folded, shipped flat. Scan is an example. Full scan of front and back available upon request.
Issued 1951 by the National Tuberculosis Association. Designed by Robert Stephens. Image of Santa face. Printed by Eureka Specialty Printing 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.