Overview
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 upon 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 is visible to anyone on 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.
The dead drop is often used as a cut-out device. In this use the operatives who use the device to communicate or exchange materials or information do not know one another and should never see one another. While this type of device is useful in preventing the capture of an entire espionage network, it is not foolproof. If the lower level operative is compromised he may reveal the location and signal for the use of the dead drop. Then the counter espionage agents simply use the signal to indicate that the dead drop is ready for pickup. They then keep the spot under continuous surveillance until it is picked up. They can then capture the operative who picked up the material from the dead drop.
The dead drop spike is a concealment device similar to a microcache which has been used since the late 1960s to hide money, maps, documents, microfilm, and other items. The spike is waterproof and mildew-proof and can be shoved into the ground or placed in a shallow stream to be retrieved at a later time.
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