Number sign


The symbol is known as the number sign, hash, or pound sign. The symbol has historically been used for a wide range of purposes, including the designation of an ordinal number and as a ligatured abbreviation for pounds avoirdupois – having been derived from the now-rare.
Since 2007, widespread usage of the symbol to introduce metadata tags on social media platforms has led to such tags being known as "hashtags", and from that, the symbol itself is sometimes called a hashtag.
The symbol is distinguished from similar symbols by its combination of level horizontal strokes and right-tilting vertical strokes.

History

It is believed that the symbol traces its origins to the symbol, an abbreviation of the Roman term libra pondo, which translates as "pound weight". This abbreviation was printed with a dedicated ligature type, with a horizontal line across, so that the lowercase letter would not be mistaken for the numeral. Ultimately, the symbol was reduced for clarity as an overlay of two horizontal strokes "=" across two slash-like strokes "//". Examples of it being used to indicate pounds exist at least as far back as 1850.
The symbol is described as the "number" character in an 1853 treatise on bookkeeping, and its double meaning is described in a bookkeeping text from 1880. The instruction manual of the Blickensderfer model 5 typewriter appears to refer to the symbol as the "number mark". Some early-20th-century U.S. sources refer to it as the "number sign", although this could also refer to the numero sign. A 1917 manual distinguishes between two uses of the sign: "number "; and "pounds ". The use of the phrase "pound sign" to refer to this symbol is found from 1932 in U.S. usage.
The term hash sign is found in South African writings from the late 1960s, and from other non-North-American sources in the 1970s.
The symbol appears to have been used primarily in handwritten material; in the printing business, the numero symbol and barred-lb are used for "number" and "pounds" respectively.
For mechanical devices, the symbol appeared on the keyboard of the Remington Standard typewriter, but was not used on the keyboards used for typesetting. It appeared in many of the early teleprinter codes and from there was copied to ASCII, which made it available on computers and thus caused many more uses to be found for the character. The symbol was introduced on the bottom right button of touch-tone keypads in 1968, but that button was not extensively used until the advent of large scale voicemail in the early 1980s.

Usage in information technology

The number sign is often used in information technology to highlight a special meaning. It was adopted for use within internet relay chat networks circa 1988 to label groups and topics. This usage inspired Chris Messina to propose a similar system to be used on Twitter to tag topics of interest on the microblogging network. Although the hashtag started out most popularly on Twitter as the main social media platform for this use, the use has extended to other social media sites.

Usage in North America

Mainstream use in the United States is as follows: when it prefixes a number, it is read as "number", as in "a #2 pencil". The one exception is with the "#" key on a phone, which is commonly referred to as the pound key or pound. Thus instructions to dial an extension such as #77 are commonly read as "pound seven seven".
In Canada the symbol is called both the number sign and the pound sign or pound key. The American company Avaya has an option in their programming to denote Canadian English, which in turn instructs the system to say number sign to callers instead of pound sign.

Usage in the United Kingdom and Ireland

In the United Kingdom and Ireland, it is generally called a hash. It is not used to denote pounds, either as weight or currency. It is not called the pound sign; that term is understood to mean the currency symbol.
The use of as an abbreviation for "number" may be understood in Britain and Ireland, where there has been business or educational contact with American usage, but use in print is rare. British typewriters had a key where American typewriters had a key. Where Americans might write "Symphony #5", the British and Irish are more likely to write "Symphony No. 5".
To add to the confusion between and, in BS 4730, 0x23 represents, whereas in ASCII, it represents, thus it was common for the same binary code to display as on US equipment and on British equipment.

Other names in English

The symbol has many other names in English:
; Comment sign: Taken from its use in many shell scripts and some programming languages to start comments.
; Hash mark
; Hashtag, or hashtag symbol: The word hashtag is often used when reading social media messages aloud, indicating the start of a hashtag. For instance, the text "#foo" is often read out loud as "hashtag, foo". This leads to the common belief that the symbol itself is called hashtag. Twitter documentation refers to it as "the hashtag symbol".
; Hex: Common usage in Singapore and Malaysia, as spoken by many recorded telephone directory-assistance menus: "Please enter your phone number followed by the hex key". The term hex is discouraged in Singapore in favour of hash. In Singapore, a hash is also called hex in apartment addresses, where it precedes the floor number.
; Octothorp, octothorpe, octathorp, octatherp
; Sharp: Resemblance to the glyph used in music notation, U+266F. So called in the name of the Microsoft programming languages C#, J# and F#. Microsoft says, "It's not the 'hash' symbol as most people believe. It's actually supposed to be the musical sharp symbol. However, because the sharp symbol is not present on the standard keyboard, it's easier to type the hash symbol. The name of the language is, of course, pronounced 'see sharp'." According to the ECMA-334 C# Language Specification, section 6, Acronyms and abbreviations, the name of the language is written "C#" followed by the NUMBER SIGN # and pronounced "C Sharp".
; : Used in proof-reading to denote that a space should be inserted. This can mean
; Square: Occasionally used in the UK – especially during the Prestel era, when the symbol was a page address delimiter. The International Telecommunications Union specification ITU-T E.161 3.2.2 states: "The symbol is to be known as a 'square' or the most commonly used equivalent term in other languages". Formally, this is not a number sign but rather another character, the.
; Gate: From the 1960s to the 1990s the British telephone company, the GPO and its successors Post Office Telecommunications and British Telecom referred to this as gate on telephone keypads.
; Others: tic tac toe, crosshatch, fence, mesh, flash, grid, pig-pen, tictactoe, scratch , gate, hak, oof, rake, crunch, punch mark, sink, corridor, capital 3, and waffle.

In mathematics

In Unicode, several # characters are assigned. Other attested names in Unicode are: pound sign, hash, crosshatch, octothorpe.
At least three orthographically distinct number signs from other languages are also assigned:
On the standard US keyboard layout, the symbol is. On standard UK and some other European keyboards, the same keystrokes produce the pound sign, symbol, and may be moved to a separate key above the right shift key. If there is no key, the symbol can be produced on Windows with, on Mac OS with, and on Linux with.