Dead Drops Project

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.
The location of the dead drop could be a loose brick in a wall, a library book, a hole in a tree, or under a boulder etc. It should be something common and from which the items can be picked up without the operatives being seen by a member of the public or the security forces who may be watching.