it first caught my eye because of the luster then I started looking closer at the date. and something is up with the reverse as well. I didn't notice the reverse until I uploaded pics I was to focused on the date.
The reverse die might have accumulated a light coating of debris-filled grease which created the "scratchy" texture in the field from STATES downward toward ONE CENT. It looks like the grease and debris may have partially filled the "E P" of E PLURIBUS, did the same on the steps of the Memorial and the "E" of CENT. I'm not sure about the date, and the markings on on the "97" appear to be raised (I think) which would rule out a clash. Maybe it's a die gouge or something, but the mark on the "9" looks strangely similar to the mintmark. Chris
According to Alan Herbert, The filling in a letter or digit becomes very hard from the repeated pressure of the striking so when it falls out it retains its shape, and, typically when struck into a coin, will form a shallow, rounded impression of the original letter, digit or other design element. What Herbert doesn't say is whether a retained strikethrough element will completely imbed itself flush with the surface of the field or if the rounded shape can appear to be partially above the surface of the field. Note that this mark on the Lincoln cent has a rounded upper surface that would conform with the rounded incuse design of the mintmark. I don't know for sure because I have never seen one, so I am just throwing out a possible theory. Chris
This is die gouges , a tiny one on the left side of the 9 and another tiny one on the right side of the 9. same as the one on the right side of the seven. These darn die gouges can appear in certain ways to really confuse us. I have a state quarter with a huge die gouge at he end of Washingtons chin that is not touching the chin and looks almost exactly like another chin. this one can easily be seen with the naked eye.