These "defiance leads" are from the roof of the Oude Kerk. The term comes from defy, or resist. In fact, the pieces of lead were used to stop water seeping in around nail holes and thus prevent rusting. They were used by plumbers as a kind of business card and were therefore stamped with initials and guild stamps. Such is the case on three of these plaques, which depict a crossed hammer and rod, combined with letters representing a year and hallmark. On four other shields, the coat of arms of Amsterdam, with its three St. Andrew's crosses, is clearly recognizable.