Yorick, what you are showing is the 6 from a small date 1960 coin.There were major issues with both the small and large date 1960 dies, as it is believed that the master die for these two were created from the 1959 master hub and then re-engraved. The small and large date had major issues that you will see across P,D, and proofs and throughout the obverse, not just the date.
Back to what you are referring too though. On top of your 6, there is shipping showing but I do not think that is what you are referring to, it's the "knob" on the inside that protrudes inward. This is part of the poor re-engraving job that I spoke of and a pic below will show this pointed out (from an article by B.J. Neff). I have also included that article, along with another from Error-Ref that will explain this more in depth. After reviewing this, let us know if you have any more questions.
Article from LCF
https://www.lincolncentforum.com/ob...-small-date/ Article from Error-Ref.
https://www.error-ref.com/the-myste...incoln-cent/ 
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