Dead Drops Project

Originally a dead drop or dead letter box, is a location used to secretly pass items between two people, without requiring them to meet. This stands in contrast to the live drop, so called because two live persons meet to exchange items or information.
Spies have been known to use dead drops, using various techniques to hide items (such as money, secrets or instructions) and to signal that the drop has been made.
The system involves using signals and locations which have been agreed in advance. These signals and locations must be common everyday things to which most people would not give a second glance. The signal may or may not be located close to the dead drop itself.