1948 D Jefferson Nickle Strange marking mint error?

This nickle has a strange inner circle stamped on both sides. It is very clear on the back of the nickle and on the front you can see it but have to look a little harder due to wear. I have not come across this before. Could this be a mint error? Any help and/or advice is greatly appreciated. Pics are attached.

Thanks
Cecilia

 

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Damaged. Definitely not a mint error.

 

Those are from coin rolls machine. Its PMD.

 

Looks like more than a coin rolling machine. But definitely damaged after it left the mint.

 

I am sorry I am very new and just barely started collecting. PMD? Please don't make fun for me not knowing this if it is supposed to be obvious like i said I am brand new to the whole coin world

 

(PMD) Post Mint damaged. It damaged after it left the mint. No worries, we all been there. Stick around and you will learned more. As we are still learning everyday.

 

PMD = Post Mint Damage.
meaning it was damaged after it left the mint.
Damage can be unlimited
whereas a Mint Error is limited and most are known.