The first paper currency issued by the Department of the Treasury were Demand Notes Series 1861. The original "Greenback" was created during the Lincoln Administration. It is considered by some to be a "fiat currency" because its value is not connected to gold or silver. The first series Greenback is exchangeable for a government bond that pays 6 per cent interest per annum. The Greenback came with a red seal.

 

The above image is a counterfeit 1862 note. It was printed on legitimate paper, but has no red seal. Therefore, it is counterfeit.