The currency sign (¤) is a character used to denote an unspecified currency. It is often used in place of a symbol that is not present in the font in use; for example, in place of the Colón (₡). It can be described as a circle the size of a lowercase character with four short radiating arms at 45° (NE), 135° (SE), 225°, (SW) and 315° (NW). It is slightly raised above the baseline. It is represented in Unicode as U+00A4¤currency sign (HTML: ¤¤).
The currency sign was once a part of the Mac OS Roman character set, but Apple changed the symbol at that code point to the euro sign (€) in Mac OS 8.5. In non-Unicode Windows character sets, the euro sign was introduced as a new code point. In the Unicode character set, each of the two symbols has its own unique code point across all platforms.
The symbol is available on some keyboard layouts, for example French, Danish, Norwegian, Swedish, Finnish and Estonian.
The symbol was first encoded for computers in 1972, as a replacement for the dollar sign in national variants (ISO 646) of ASCII and the International Reference Variant. It was proposed by Italy to allow an alternative to encoding the dollar sign. When ISO 8859 was standardized, it was placed at 0xA4 in the Latin, Arabic and Hebrew character sets. There was not room for it in the Cyrillic set, and it was not included in all later added Latin sets. In particular, Latin 9 replaces it with the euro sign. In Soviet computer systems (usually using some variant of KOI8-R character set) this symbol was placed at the code point used by the dollar sign in ASCII.
Even when it is appropriately used, it has an inherent ambiguous meaning; ¤12.50 can be interpreted as 12.5 units of some currency, but the currency itself is unknown, and can only be determined by information outside the use of the character in itself.
More likely, this sign was intended to mark the position of the national currency symbol into the national variants of ASCII (7-bit, 95 printable characters available), where a specific national body was reluctant to accept the dollar sign ($) as a kind of "universal sign" to denote "currency" or "money". The currency sign ¤ should then be replaced by the appropriate glyph, depending on audience (₤, ¥, ฿, ₱ etc.). But somehow, the neutral currency sign (¤) was to be used as a printable symbol in itself, and this usage was sufficiently extended in the years of the first drafts of ISO 8859 to include it.
Using one and the same code point for different national currency symbols can be problematic in international communication. If, for example, an amount of £100 is written in an e-mail or on a website, and the software does not make sure that the same character set is used at both ends, it could be interpreted e.g. as ¥100, which is a much lower value than £100. (To put this into perspective, as of May 2014, ¥100 is worth approximately £0.58.)
In some versions of BASIC (notably in ABC 80 BASIC and ABC 800 BASIC), the currency sign was used for string variables instead of the dollar sign. It was located on the keyboard and the character set table at the same position in many national keyboards (like Scandinavian) and eq versions of 7-bit ISO/IEC 646 ASCII, as the dollar sign is in US-ASCII.