大家都知道，$表示美元。那么它是怎樣來的呢?一種說法是，它是PS疊合寫法的演變。PS是18至19世紀期間美國的一種圓形硬幣比索(Pesos)的縮寫，這種硬幣在1974年美國正式建立造幣廠以前一直在全國通用。后來美國政府認可了$這個符號作為新貨幣的一個單位，即一美元。在書寫時，$要擺在數字前面。如1美元應寫成$1，50美元寫成$50。而這種寫法的背后還有一個小故事。

It is only appropriate that an Irish immigrant to the United States be the one credited with originating the dollar sign. Oliver Pollock sailed the high seas at the age of twenty-three, and settled in Carlisle, Pennsylvania. This young entrepreneur rapidly established himself as a wealthy and influential West Indies trader.

Pollock moved his operation to Louisiana, where he amassed even more wealth as a trader, and as a plantation owner. His success enabled him to provide supplies to the Patriots' cause in the Revolutionary War, and to maintain close contact and a degree of influence with Congress. Pollock's success allowed him easily to purchase military supplies to support "the cause," as the Spanish Empire had an outpost in New Orleans, Louisiana. In his dealings with the Spaniards, Pollock used their currency, the peso.

In true Spanish tradition, Pollock used an abbreviation for pesos, yet his penmanship made the abbreviation appear to be the transposition of the letters "p" and "s."

Prior to 1775, the fledgling nations monetary system was in disarray, and needed to be revamped. By 1775, Congress decided to rectify the situation by backing all of its legal tender with the most commonly circulated coins that were, coincidentally, Spanish coins minted in the New World. Americans then began trading with "Spanish milled dollars," later termed "dollars," as Americans shed the "pounds" that were the vestiges of British rule.

Congressman Robert Morris, to whom Pollock addressed his billing records, perpetuated the use of the dollar sign, and was the first high government official to give his blessing to the "s" with the two lines through it.

The appearance of the dollar sign in print, in a 1797 book by Chauncey Lee, signified the acceptance of the dollar as a purely American symbol.