Also known as "Tackamarks" and "Tacmars", basically meaning "
tactical markings".
Conspiracy theorists believe these to be coded symbols which the
military may use to control the
populace in the event of
civil unrest.
The American
DOT road sign dating program is believed to be part of this.
Reflective stickers are attached to the back of
road signs to indicate the date the road sign was
installed. It is believed that positioning of these
stickers indicates locations of
strategic importance.
Another example of tacmarks in the United States is the positioning of
clusters of
road signs, and the introduction of European-style road signs (involving symbols instead of plain English), such as the slashed 'P' to indicate no parking, most American signs to indicate no parking areas simply say "no parking" in plain English. It is believed that these slashed 'P' signs indicate important
resources for
military use.
Some of these theories have actually worked. Harold R. Green of "Free Indeed Research" claims to be able to follow coded tacmars to places such as helicopter landing areas, and detention facilities. His website is at:
http://tackamarks.freeservers.com
While containing a lot of evangelistic christian content, his website is actually rather interesting. It explains his "quadrant sign code" and "Operation Garden Plot" theories.