50-1x, WX150, 1950 U.S. National Christmas Seals Sheet, pm E, full gum, F, MNH. Firm, fresh, never foded, shipped flat. Scan is of a full sheet.
Issued 1950 by the National Tuberculosis Association (NTA). Designed by Andre Dugo. Image of three young carolers, sheet of 100 (10x10) seals; colors: red, green, yellow, and black. Seal size: 21x26mm. Printer's Mark "E" on the green background below the double-barred cross, in the lower left corner of seal #56.
Christmas Seals are also known as TB Charity Seals, and are usually classified as Charity Seals, or Cinderella Stamps.