Regarding the ‘#’ sign used to abbreviate it, in some regions of the United States and Canada, the symbol is traditionally called the pound sign, but in others, the number sign. This derives from a series of abbreviations for pound, which is a unit of mass or weight. At first “lb.” was used; later, printers got a special font made up of an “lb” with a line through the ascenders so that the lowercase letter “l” would not be mistaken for the number “1”. Unicode character U+2114 (℔) is called the “LB Bar Symbol,” and it is a cursive development of this symbol. Finally came the reduction to a combination of two horizontal (cf. skewed “=”) and two forward-slash-like (cf. “//”) strokes (in this respect, names like fence or square, as well as the representation of the sign containing two exactly vertical instead of slanted strokes, as in many keyboards, including cell-phones’, are misleading).

Its traditional commercial use in the U.S. was such that when it followed a number, it was to be read as “pounds”, as in 5# of sugar, and when it preceded a number, it was to be read ‘number’, as in #2 pencil. Thus the same character in a printer’s type case had two uses.