21-2x, WX29, 1921 U.S. Christmas Seals Sheet, Type 2, full gum, F, MNH. Never folded, shipped flat.
Issued 1921 by the National Tuberculosis Association (NTA). Designed by George V. Curtis. Image of Santa and two children in a chimney. Sheet of 100 (10x10) seals; Colors: Green, blue and red; seal size: 19x19mm; perf. 121/2. Dots in red shading, arranged in horizontal rows, identify this as Type 2 seals. Printed by Strobridge Lithographing Co.
Christmas Seals are also known as TB Charity Seals, and are usually classified as Charity Seals, or Cinderella Stamps.