Dead Drops Project

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.
The signaling devices can include a chalk mark on a wall, a piece of chewing-gum on a lamppost, a newspaper left on a park bench etc. Alternatively, the signal can be made from inside the agent's own home e.g. hanging a distinctively colored towel from a balcony, or placing a potted plant on a window sill where it can be seen by anyone driving down the street.
Aldrich Ames left chalk marks on a mail box located at 37th and R Streets NW in Washington, D.C. to signal his Russian handlers that he had made a dead drop. The number of marks on the box prompted some local residents to speculate, somewhat jokingly, that it was used by spies.