Two stamped envelopes, first day of issue, in honor of Marc Chagall, with his signature, 1967, 1983. * Official United Nations envelope, first day of issue, in honor of Chagall’s windows, 1967, with Chagall’s penciled signature. In 1961, the Secretary-General of the United Nations, Dag Hammarskjöld and fifteen peacekeepers were killed during a peace mission in Zimbabwe. In their memory, Chagall created stained glass windows that were installed in the lobby of the United Nations in 1967. The United Nations issued this stamp that same year. * “Chagall Windows” envelope, on the first day of issue of the Israeli stamps featuring the twelve tribes in 1973. The envelope bears Chagall’s penciled signatures and two stamps from the tribes of Joseph and Benjamin.