The Unicode standard calls the symbol “Prescription Take”. The Wikipedia page for Rx says that Rx is the symbol for medical prescriptions. (Wikipedia also gives a numismatic meaning: Rx means “tens of Rupees”).
The Straight Dope, Cecil Adams’ newspaper column, gives the medical history of the Rx symbol. There is controversy among pharmacy historians. There are three theories. 1. “Rx is an abbreviation for the Latin word ‘recipere’ or ‘recipe,’ which means ‘Take, thou.’”. 2. Rx is the astrological symbol for the god Jupiter. 3. Rx comes from the Egyptian symbol for the left Eye of Horus.
None of these sources explains why ℞ would be used in numismatic works to mean “reverse”. Barclay Head isn’t the only writer to use the symbol, it was also used by French writers Mionnet and Babelon in the 19th century. It is always followed by a period.
Another odd symbol was used in the 18th century. J. H. Eckhel used a symbol that looks like a cross between mismatched parenthesis, )(, and an asterisk to mean “reverse”. For example, volume 2 page 209 of Eckhel’s Doctrina numorum veterum (1792). I don’t know the name for this symbol, or if it was ever used non-numismatically. Eckhel also used )( without the decoration – perhaps his publishers didn’t have enough of the rare symbol to set type? At least one English-language author used the symbol in the reversed parenthesis form, R. S. Conway (The Italic Dialects (1897), for example p. 14).
Speculations: Eckhel’s reverse symbol is 1. a decorative version of actual mismatched parenthesis, 2. a decorative version of the Roman ‘Denarius Sign’ (an X with a line through it), or 3. a version of the Pisces astrological symbol without a space between the fishes. The problem with these theories is that the symbol doesn't look much like any of them. Pisces makes the most sense, as the Pisces symbol is supposed to represent two connected fishes swimming in opposite directions.
I would enjoy corresponding with anyone on this topic.
