What does the A in a 1934 A US 10 dollar bill mean?

Answer 1

The letter next to the date on any US bill is called the series letter. It indicates how many major changes have been made to some aspect of the bill since the series started.

It indicates which pairing of Treasury Secretary and US Treasurer were in office when that particular run of bills was first printed. The "A" on a 1934 $10 bill means it was printed during the run begun when Henry Morgenthau was Treasury Secretary and William A. Julian was Treasurer; i.e. somewhere in the period between January 1934 and July 1945

So if it could have been printed in 1945, why does the bill have a 1934 date on it? Unlike dates on coins, the dates on US bills aren't necessarily the year they were printed. They indicate the start of what's called a "series". The letter is a kind of subseries within the series year.

Up till 1974, a series date represented the year that a particular design was adopted. The series date stayed the same until that particular design was replaced. When a new Treasury Secretary or US Treasurer was appointed, a small letter would be put next to the date. The start of the series had no letter. When a new official was appointed an A would be added, then a B, C, and so on. "A" is the first letter which means your bill was printed as part of the second subseries, because the first one didn't have a letter.

While most denominations were redesigned somewhat regularly and thus got new series dates, 1935-series $1 bills were never updated. The date was kept the same while the series letter just kept incrementing with every signature change, for some 30-odd years. The absurd situation of 1935-dated bills being printed into the 1960s led to new policy in 1974. Since then, the series date is changed whenever a new Treasury Secretary is appointed, in addition to whenever there's a new design. The series letter now increments only when or if a new Treasurer is appointed during that series year.