I found this quarter out of a vending machine, there is a small "A" on the front of it, you may have to zoom in.
Sarcasm from Kirkuleez. A counter stamp is just when something was stamped into the coin. You could get a piece of steel in the shape of an A and hit it with a hammer so it leaves that mark in the coin.
I saw..........nothing. A counter stamp would be more obvious and prominent. Perhaps an anomaly resembling an 'A'? Or more likely, post mint damage resembling an 'A'.
It looks like it is a counterstamp to me. That A was not there when the coin was issued from the mint.