A star on any US bill means that it was issued as a replacement for a bill that was damaged during printing.
The damaged bill (or more often, bills) will be removed from the set and destroyed. The mechanism that prints individual serial numbers makes it difficult to print new bills with the exact same numbers as those that were destroyed. Instead, a special print run is made to replace all damaged bills at the same time. That print run has its own set of serial numbers, but the starting or ending character is a star rather than a letter to indicate that the bills aren't from the original printing.
Because "star notes" are uncommon many collectors will pay a premium for them. The amount varies with the bill's denomination and condition. A worn $1 star note may only bring 25¢ to $1 extra, but an uncirculated $100 star note could sell for significantly more than its face value.
A star in a serial number on any U.S. banknote indicates that the original bill with that number was damaged, and the star note is the replacement.
That's called a star note. The star at the end of the serial number indicates that the original bill was damaged during printing and was then replaced.
It is worth ≈ $10
Depends on year condition etc.
A silver certificate star-note would normally be worth around $5 or so, depending on how worn it is.
Less than 11% of all the 1957 series Silver Certificates have the star by the serial no. If your Silver Certificate is in choice crisp condition it is worth $40.00. In circulated condition, it's worth about $5.00
About $3.
A star in the serial number of any bill, not just a silver certificate, means that the original bill bearing that serial number had a defect and was destroyed. Because bills are printed in large groups it's impractical to reprint specific serial numbers. Instead, a new set of serial numbers is started and a star is added to indicate that these notes are replacements. Collectors generally prefer star notes and it may make the bill be worth a bit more.
How much is a 1957a silver certificate worth?
If you mean a $5.00 silver certificate a crisp an well centered bill about $12.00 to $15.00.
About $25. If there is a star in the serial number, about $40.
About $9 - $10 if it is in uncirculated condition.