The sign is first attested in business correspondence in the 1770s as a scribal abbreviation "ps", referring to the Spanish American peso, that is, the "Spanish dollar" as it was known in British North America. These late eighteenth- and early nineteenth-century manuscripts show that the s gradually came to be written over the p developing a close equivalent to the "$" mark, and this new symbol was retained to refer to the American dollar as well, once this currency was adopted in 1785 by the United States.
An alternative theory states that the dollar sign ($) is directly borrowed from the sign used to represent the Spanish peso, which is in fact a "$", and is said to come from a representation of one of the Pillars of Hercules with a motto-ribbon as depicted in the Spanish Coat-of-Arms.