@numi, assuming that you have used the tip of a wooden toothpick or similar to ensure that it isn't just a whisker stuck on top of the coin, my best guess is that it is the metal "smushed" up when a sharp blade made that small surface cut. I'm struggling to see how it could be anything but damage of some sort.
"If you climb a good tree, you get a push." -----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed." -----King Adz