medallion stamp program means: A program approved by the Securities Transfer Association that enables participating financial-institutions to guarantee signatures. Medallion programs guarantee The individual who signs the stock certificate, stock power or certificate is actually the registered owner. This information appears on either the stock certificate/stock power. Medallion Guarantees can be provided by any U.S. financial institution which is a member of the Medallion Stamp Program. These institutions can include U.S. brokerages, banks and savings and loan companies, and credit unions. (in Stock Market Dictionary)