What does a B mean on a 1957 US silver certificate?

Answer 1

A letter next to the date on any US bill (not just silver certificates) is called a "series letter", and indicates what where the bill and others like it fit into the different print runs that make up a series.

Series letters can be very confusing because they don't quite follow a natural sequence and in addition their meaning has changed over the years.

Normally the first set of bills in a series is "plain"; i.e. they don't have a series letter. When the Treasury decides to add a series letter they start with A, then B, and so on, which means that A actually indicates the second subseries, B the third, etc.

Up till 1974 the Treasury defined a series as beginning only when a bill was given a major design or production-method change. At that point the denomination's series date would change, but the date would then stay the same until the next major update. If the President appointed a new Secretary of the Treasury or US Treasurer while that series date was in effect, the letter would increase.

Because $1 bills used the same design for decades, this practice led to the absurd situation where 1935-dated bills were printed into the mid-1960s and series letters incremented almost halfway through the alphabet. The Treasury changed the criteria so a new series date would be assigned whenever a bill was updated OR a new Secretary of the Treasury was appointed. Series letters would increment only when or if a new Treasurer took office during that Secretary's term. As a result bills since the 1970s have many different series dates while series letters rarely go above B or C.

Of course like most bureaucratic practices the new rules aren't always followed exactly. There have been a few cases where designs changed without a new series date, or a series letter was skipped if no bills were printed during a particular Treasurer's term.