In 1909, Scott Perky of Niagara Falls patented a font where each letter and symbol has a vertical line of symmetry. This allows you to write a word either forwards or backwards without needing to change or reverse the characters.
In his patent filing — which is online here and is quite delightful to read — Perky notes that his font would allow you to print a document with each line going in the opposite direction. — Read the rest
