The letter next to the date on the silver certificate What does it mean?

It's called a series letter. Series letters can be used on any type and denomination of bill.

Dates on U.S. currency don't indicate the year in which the bill was printed, only the series. The factors that determine a series have changed over the years. It used to be that a new series was introduced only when a bill's design changed. When a new treasury secretary or new treasurer was appointed, a letter was placed after the date. The lack of design changes during the 20th century produced some ridiculously long series. For ex. the 1935 series of silver certificates was printed into the late 1950s, with series letters going up to H.

Now, the series is linked to the treasury secretary - when a new person is appointed, the bills have a new series date. When the treasurer (a secondary office) changes, the same series date is kept, but the letter changes.

Regardless of which practice is used, the first bills in a series have no letter. An A is appended only after there is a change in cabinet officers, so an "A" bill is really the second in the series, a "B" bill is third, etc.

These practices have produced some anomalies - for example there are 2004A $10 bills but no 2004 tens because no tens were printed during the term of office of the first treasurer who served Secretary John Snow. But there are also two differentdesigns of $5 bill with the same series because the same treasurer was in office during the time that each design was issued!