Whilst even the internet cannot put a precise date on the date of the invention of the first magnetic signs, there is a popular legend surrounding the discovery of magnets. Sometime around 4,000 years ago, a Cretan shepherd called Magnes was, perhaps unsurprisingly, herding his sheep in an area of what is now northern Greece when the nails in his shoes and the tip of his staff became firmly stuck to the large black rock on which he was standing. He dug up the earth around the rock and discovered a lodestone, which contained magnetite, a natural magnetic material.
Following on from a Greek shepherd, further investigation of magnets and magnetism was continued by the Greeks, by the Chinese (who developed the mariners compass) and Peter Peregrinus de Maricourt, a 13th century French scientist and scholar who wrote the first treatise describing the properties of magnets. However, significant progress was made only with the experiments of William Gilbert, an English physician, physicist and natural philosopher. In 1600, it was Gilbert who first realised that the Earth was a giant magnet and that magnets could be manufactured by beating wrought iron.
In 1820, Hans Christian Oersted, a Danish physicist and chemist, discovered that electric currents create magnetic fields. Eventually, it was James Clerk Maxwell, a Scottish mathematical physicist, who formulated a set of equations that describe electricity, magnetism and optics as manifestations of the same phenomenon, namely the electromagnetic field. Maxwell's achievements concerning electromagnetism have been called the "second great unification in physics," after the first one realised by Isaac Newton. What is more remarkable is that Maxwell developed his ideas in 1862, more than thirty years before the discovery of the electron in 1897, a particle that is so fundamental to the current understanding of both electricity and magnetism. It was but a short jump from there to fridge magnets.
Fridge magnets are most undoubtedly magnetic signs at their most abundant. Whilst it feels like these little, usually whimsical, ornaments have been with us forever (well, as least since just after the invention of the refrigerator), it is reported that the first fridge magnet patent was obtained only in the 1970s by a William Zimmerman of St. Louis, Missouri. The largest collection of fridge magnets, according to the Guinness World of Records, is owned by a Louise J. Greenfarb and, as of January 2009, numbered some 40,000 items. As magnetic signs go, fridge magnets are the smallest but, still, that number must require some significant storage space. However innocuous the object, there is always someone, somewhere, who collects them. Just ask the lady who collects banana labels (13,552 and counting!).
The main purpose of a sign is to communicate, to convey information, and can be roughly divided into the following functions: information, direction, identification, safety, and regulatory. Magnetic signs are particularly useful where signs are not intended to be permanent and where they might be put up and taken down at regular intervals. They will adhere to anything with a steel surface, such as shelving or filing cabinets, but they really come into their own on the sides of vehicles such as lorries and taxis.