UNITED STATES C13-15 USED ON COVERS. Another quality product from Randy Scholl Stamp Company. All credit cards will be charged in US Dollars. Returning Items must arrive back to us within 30 days to be covered by this policy. Randy Scholl Stamp Company. The item “UNITED STATES C13-15 USED ON COVERS” is in sale since Monday, January 8, 2018. This item is in the category “Stamps\United States\Back of Book\Air Mail”. The seller is “rschollstamp” and is located in Cincinnati, Ohio. This item can be shipped worldwide.