1909 plain Lincoln cent. Noticed this imperfection, and it looks to me like a lamination error. Just wanted other opinions.
The coin has some small PMD spots but the area you are referring to looks like a small detached lamination.
Handsome coin. Get out a toothpick and try to dislodge some of that verdigris while it's still trying to hang on. It looks like it can still loosen off. Just be gentle and take your time with it. No oils or solvents, just distilled water if you need to moisten the toothpick.