United States 1967/1967 - Marc Chagall Window

UN collector's item from 1967 for the issue “Chagall Window” based on the famous work by Marc Chagall (1887–1985).
The item bears a handwritten signature attributed to Marc Chagall. The signature, however, has not been professionally examined or certified, and therefore no warranty of authenticity is conveyed.
An attractive collectible that connects art history and philately.
Age-appropriate condition. Please refer to the photos regarding the signature, cancellation, and preservation. The images are part of the description.