1961-3px, 1961 U.S. Christmas TB Seals, Imperforate Proof Sheet of 100 seals, pm "F", F, No Gum. Firm paper, fresh, never folded, shipped flat. Scan is an example. Full scan of front and back available upon request.
Issued 1961 by the National Tuberculosis Association (NTA). Designed by Heidi Brandt. Images of holiday family life, in blocks of four (4), alternating throughout sheet. Printed by Fleming-Potter Company.
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.