The currency sign (¤) is a character used to denote an unspecified currency. It is sometimes called scarab. 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 raised slightly above the baseline. It is represented in Unicode as U+00A4 ¤ CURRENCY SIGN (HTML
¤ · Windows Alt+0164).
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.
Currency sign (typography) Wikipedia
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.
When it is appropriately used, for example ¤12.50 can be interpreted as 12.5 units of some currency, but the currency itself is unknown, and can be determined only by information outside the use of the character in itself. Such dependence on context is called deixis. Widely used other words (for example I, here, now) also have a meaning depending on context. Therefore this sign is a sort of pronoun.
In international text-based discourse, such as international trading or listing exchange rates, it is not uncommon to refer to a given currency with its three-letter ISO 4217 code instead of or in conjunction with a currency symbol, to avoid ambiguity as using 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 12 July 2015, 5:30AM +0 ¥100 is worth approximately £0.72.)
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". 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.