What series is a 1976 US 2 dollar bill?

Answer 1

The series of a bill in US currency refers to when the bill was last redesigned, not to the year it was printed, so 1976 IS the series.

The bill was redesigned in 1976 (the front looks pretty much the same, except that different people were Treasurer and Secretary of the Treasury than the last time the bill had been printed, and the 1976 serial numbers were printed in green rather than red, but the back is entirely different), so it's "Series 1976".

By convention, the year is updated for "major" changes, and a letter is added for "minor" changes. Changing the signature of the treasurer is considered a minor change; after 1974, changing the signature of the secretary of the treasury is considered a major change (prior to that, changing either signature was a minor change).

There are also series 1, series 2, etc. bills, but these are all from before the 20th century. At least by 1914 the new system where the series number represents the design year was in use, and all modern small-sized bills use this format.