It's called a counterstamp. It has been intentionally stamped after the coin left the mint. There are hundreds of different ones out there. Anyone with a punch can create one.
@joedad, that is an interesting counterstamp. While I can't find a match, here are all the prior CCF threads with other types of star counterstamps that I can find:
Disclaimer: While a tremendous amount of effort goes into ensuring the accuracy of the information contained in this site, Coin Community assumes no liability for errors. Copyright 2005 - 2026 Coin Community Family- all rights reserved worldwide. Use of any images or content on this website without prior written permission of Coin Community or the original lender is strictly prohibited. Contact Us | Advertise Here | Privacy Policy / Terms of Use