This type of paper currency was introduced to the U.S citizens in 1878. According to the law, the "unusual" dollar could be exchanged to silver bars or coins of the same material. Actually, they looked like the ordinary U.S currency notes (dollars) but instead of the phrase "Federal Reserve note" they had "Silver Certificate" on them. The last bank notes of this kind were printed in 1964 but they stopped being an official currency only in 1968. Though, even nowadays people may use them as the legal tender.

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