Dead Drops

A dead drop (or dead letter box) is a method of espionage tradecraft used to pass items or information between two individuals (e.g., a case officer and an agent, or two agents) using a secret location, thus not requiring them to meet directly and thereby maintaining operational security.

A dead drop is simply an agreed upon spot where you or your contact can leave a message for the other without actually meeting in person. These are typically used in conjunction with a "Signpost," or a place to leave a signal that the message has been dropped.

Of course, you do not need to be engaged in espionage to make use of a dead drop.  Anytime you need a clandestine way to pass messages or materials to someone, the dead drop can be used.

Dead drops need to be arranged in advance. Find locations where you can place and retrieve materials without being seen. The dead drop location should be easily accessible, 24 hours per day, and should be relatively easy to access. At the same time however, the dead drop location should not be a place where a passer-by, children playing, or others are likely to discover or disrupt it.

The signpost is a place where a signal is left when the dead drop is loaded (load signal) and a second signpost is used to indicate that the dead dropped material has been recovered (unload signal).  The signpost need not be an actual signpost, rather it is anything that signals a change in the dead drop condition. A mark of chalk on the corner of a building is a common signpost method, but you can no doubt think of many other signals.

A couple of YouTube videos describe dead drops.

Above the Tearline: Brush Passes and Dead Drops

Black Scout Tradecraft- How to Use a Dead Drop 

Ghost: Confessions of a Counterterrorism Agent
by: Fred Burton