What is the rarest OS map symbols?

The rarest OS map symbols include those representing unique features or historical sites that are not commonly found, such as ancient monuments, certain types of wildlife habitats, or specialized land use symbols. For example, symbols indicating Roman ruins or specific archaeological sites can be quite rare. Additionally, some symbols used for temporary features, like festivals or events, may also be considered rare since they are not permanent fixtures on the landscape. Collectors and enthusiasts often seek out these unique symbols for their historical and cultural significance.