I think it was
Struck Through Grease or something like that, it's not that uncommon to see it on IHCs. I do think this coin has a weak strike, particularly on the headband after "Liberty" and on the last two feathers by the top of the neck. Detail is really lacking, but to me, it doesn't appear to be wear. I'm not saying there is no wear, this coin is definitely not MS, but these CuNi IHCs are notorious for weak strikes.