FYI Starting in the 1990s, due to the increasing prevalence of identity theft and fraud, the security measures used for these stamps increased. They now contain a barcode, and have an invisible security compound in the ink that can be read by special “Stamp 2000 Plus” scanners used by transfer agents. They also have a prefix that indicates their surety limit, which limits how much they can guarantee the transaction for: Medallion Surety Limit