21-3x, WX29, 1921 U.S. Christmas Seals Sheet, Type 3, F, No Gum. 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. Same as Type 1. Dots in red shading, arranged in diagonal rows plus seal flaws identify this as Type 3 seals. Typographed by Zeese-Wilkinson Company, Inc.
Christmas Seals are also known as TB Charity Seals, and are usually classified as Charity Seals, or Cinderella Stamps.