Since this coin is copper-plated zinc, sometimes the plating is too thin and when the coin is struck, the plating splits under the pressure and shows the underlying zinc core (grey color). It is not uncommon to see on the mintmark and will be in the direction of the rim (southeast in this case).
I'm not an expert on repunched mintmarks (RPMs) so maybe someone else will give an opinion. Clearer pics of it may be needed, I don't know.
I hope that helps.