The doubloon (from Spanish doblón, meaning "double"), was a two-escudo or 32-reales gold coin, weighing 6.77 grams (0.218 troy ounces). Doubloons were minted in Spain, Mexico, Peru, and Nueva Granada. The term was first used to describe the golden excelente either because of its value of two ducats or because of the double portrait of Ferdinand and Isabella.
Doubloons are marked as "2... S" are equivalent to $4 in US gold coins were traded in that manner. A small 1/2 Escodo coin (similar to a US $1 gold piece) have no value on them but were worth a Spanish Milled dollar in trade.
In Spain, doubloons were current up to the middle of the 19th century. Isabella II of Spain replaced an escudo-based coinage with decimal reales in 1859, and replaced the 6.77 gram doblón with a new heavier doblón worth 100 reales and weighing 8.3771 grams (0.268 troy ounces). The last Spanish doubloons (showing the denomination as 80 reales) were minted in 1849. After their independence, the former Spanish colonies Mexico, Peru and Nueva Granada continued to mint doubloons.
Doubloons have also been minted in Portuguese colonies, where they went by the name dobrão, with the same meaning.
In Europe the doubloon became the model for several other gold coins, including the French Louis d'or, the Italian doppia, the Swiss duplone, the Northern German pistole, and the Prussian Friedrich d'or.
On Pillar Spanish Dollars or Spanish Milled Dollars of the 1700's to 1899, there was a picture of the Pillars of Hercules overlaid with a scroll. This is one possible origin of the dollar sign.[1]