Dry cavers were using directional markers long before there were any cave divers. The early cave divers in Florida saw the benefit of these markers, and Lewis Holzendorf came up with the idea of folding a triangle of tape around the line to form an arrow. These tape arrows were called "Dorf" markers, in Lewis' honor.
There were a couple of problems with tape arrows, however -- they slid along the line and were difficult to feel in a silt-out. Cave diving pioneer, Sheck Exley asked fellow diver, Forrest Wilson to lead a discussion group at a NSS workshop, to come up with an idea for a better arrow. Several ideas were tossed around and eventually, Forrest came up with the current design, and hand made several hundred. Forrest’s arrows were sold through the Branford Dive Center in North Florida. They soon became very popular and Steve Hudson of PMI cave rope company asked Forrest's permission to mass produce arrows for Dive Rite.
Today, cave and wreck penetration divers from all around the world use line arrows to mark the direction of the closest exit.
Sometimes a directional marker (line arrow) is not the proper marker to leave -- Non-directional cookies mark a specific place on the line, but do not give directional information. They are preferred over line arrows for setting up traverses or circuits because they avoid the possibility of having directional markers on the line which could point away from the closest exit, which could be disastrous in an emergency. They can also offer reassurance during stressful moments. They are a must at jumps, especially jumps made from points at which no permanent marker has been installed. Placed on the outbound side of the jump, they confirm exit direction as divers return to the jump.