When Casper arrives at Potsdamer Platz, he steps on paperclips dropped on the ground by his extradition contact as a signal that the extradition might be compromised. The paperclips might be a reference to "Operation Paperclip", where the U.S. smuggled German scientists out of Germany during WWII.
Justin Marks: Series writer/creator, one of the "thugs" who drops the paperclips on the ground to tip off Casper.