The pound sign ( £) is the currency symbol for the pound sterling—the currency of the United Kingdom (UK). The same symbol is used for similarly named currencies such as the Gibraltar pound or occasionally the Syrian pound. It is also sometimes used for currencies named lira, for example the now withdrawn Italian lira.
The symbol derives from a capital "L", representing libra, the basic unit of weight in the Roman Empire, which in turn is derived from the Latin name of the same spelling for Weighing scale or a balance. The pound became an English unit of weight and was so named because it originally had the value of one tower pound (~350 grams) of fine (pure) silver. According to the Royal Mint Museum:
The pound sign is placed before the number (e.g. "£12,000") and separated from the following digits by no space or only a thin space.
The symbol ₤ (note the double dash at its middle) was called the lira sign in Italy, before the adoption of the euro. It was used (in free variation with £) as an alternative to the more usual L. or Lit. to show prices in Italian lira. It was also used unofficially as the symbol of the Maltese lira instead of the official Lm.
In American English, the term "pound sign" usually refers to the symbol number sign, and the corresponding telephone key is called the "pound key". The symbols £ and # are both referred to as the pound sign in Canadian English (# is also referred to as the "number sign" and "noughts-and-crosses board").
In the eighteenth-century Caslon metal fonts, the pound sign was identical to the italic capital "J" rotated 180 degrees.
Some fonts render the pound sign with a double bar (for example on a previous version of the British five pound note); this is simply a different glyph, and the underlying character (and therefore Unicode codepoint) is still a pound sign, and not a lira sign.
In the punched card era, equipment sold for commercial data processing in the UK needed not only to represent the pound sign, but also to handle pre-decimal currency (pounds, shillings, and pence, including halfpennies and farthings). Encodings for the necessary symbols varied by manufacturer. By the time of Decimal Day in 1971, national variants of character codes were already well established and naturally found their way into early computers.
In the computer age, prior to the introduction of 8-bit character sets in the early 1980s, the most common character code in use in the UK was the UK national variant of ISO 646, standardised as BS 4730. This code was identical to ASCII except by the substitution of two characters: x23 became "£" in place of "#", while x7E became "‾" in place of "~". Keyboards (then as now) were manufactured with different key engravings for different national markets; and printers were manufactured to support a variety of national variants of ISO 646, selectable by hardware or software configuration options.
ICL's 1900-series mainframes, used by many UK installations at the time, used a different convention, in which x24 became "£" in place of "$".
The 1980s saw the gradual adoption of 8-bit character sets designed to meet the needs of all Western European languages in a single character set: ISO/IEC 8859-1 was standardised in 1985, based on the character code used in the popular Digital Equipment Corporation VT220 terminal. This code had "£" in position xA3 (which is where it remains in Unicode). The IBM PC originally used a non-standard 8-bit character set Code page 437 in which the "£" character was encoded as x9C; adoption of ISO character codes only came later with Microsoft Windows (introduced under the misnomer "ANSI", because it was ANSI that published international standards in the United States).
Other early personal computers also adopted their own solutions. The Commodore 64 computer included a dedicated key for the pound sign (to the right of the number row). The BBC Micro used a variant of ASCII that replaced the backtick ("`", character 96, hex 60) with the pound sign, denoted as CHR$96 or (hex) CHR$&60. Since the BBC Micro used a Teletext mode as standard, this means that the pound sign is in the 7-bit ASCII variant used on Teletext systems such as Ceefax, ORACLE and Teletext Ltd as well.
On a US-International keyboard in Windows, the "£" can be entered using:
On a US-International keyboard in Linux and Unix, the "£" can be entered using:
In Windows, it can also be generated through the Alt keycodes: