a Wilkie button, or maybe a wooden nickel. (I have one around here somewhere, but can’t find to scan ! ) hehehe
I think the floor protruded past the framing and the bottom edge of the siding would not extend below the finish floor so they chiseled off that edge of the slab
Typical of poured walls. Looks like their forms didn’t hold, and then later a homeowner patch job.
Sorry guys but it was a brick ledge that was there at the time of construction but was wrong so the guys cut and hammered it away. Thought it looked interesting.