Just some kind of after market rubber stamped identification used by money changers and shopkeepers mostly done outside the US. Very popular across the big ponds. Similar to chop marks on coins.
It "appears" to be behind or under the serial number because the ink in the stamp doesn't stick to the ink used for the serial number. It's an optical illusion.
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