A curious letter is O .... not just a letter - it's often a substituted for a number - zero. It's a sphere, a circle..... though almost never a perfect circle with thankfully few exceptions.
It's one of the few letters that is the same in both upper case and lower case and there was a bit of a mystery in Toronto where the subway station names have the letter O drawn as perfect circles. Turns out the names were drawn by a draftsman and not a typographer - mystery solved.
