1921-1, WX28, 1921 U.S. Christmas TB Seals, block of 4, SE, full gum, F, MNH.
Designed by George V. Curtis. This is Type 1 of the seal, green, blue and red, 19x19mm, with perf 121/2. Scans of front and back provided for your information. Any Shading is from the scanner.
Issued by the National Tuberculosis Association.