The pound sterling sign £
The £ sign stands for the pound sterling (GBP), the currency of the United Kingdom. It comes from a capital L for libra, a Roman unit of weight, with a line across it to show it is an abbreviation. One pound is 100 pence, written with a p (50p), a system in place since decimalization in 1971.
In British English, £ goes before the amount with no space: £5, £19.99, £1.5m. Other pounds sometimes use the same sign with a prefix, such as E£ for the Egyptian pound. The lira sign ₤, with two bars, is occasionally used as a pound sign, but it is a separate character. For other money signs, see currency symbols.
Why Americans call # the pound sign
In the United States, # is commonly called the pound sign, and the # key on a phone is the "pound key". In the UK and most other English-speaking countries the same symbol is the hash, and on social media it is the hashtag symbol. In the US it was long used to mean pounds of weight, so 5# meant 5 pounds.
The name links back to ℔, a lowercase "lb" with a line through it, the old scribal abbreviation for libra, a pound by weight. A popular explanation is that # developed from a hurried ℔, though historians still debate it. Today the weight abbreviation is simply lb, as in 5 lb. More numbering signs are on the number symbols page.
How to type the pound symbol
On a UK keyboard, Shift + 3 types £ on both Windows and Mac. On a US Windows keyboard, hold Alt and type 0163 (or 156) on the number pad. On a US Mac, press Option + 3; on a UK Mac, Option + 3 types # instead.
On iPhone, £ is on the #+= symbols page, and Gboard on Android shows it on the second symbols page. In HTML, use £; in LaTeX, \pounds. The weight sign ℔ has no shortcut, so copy it here, or type 2114 and press Alt + X in Word.