Not entirely sure, but a good guess would be a Kid! Back in the day before the internet, Kids used to occupy themselves in such a manner...they would raid old Gpaws coins and then proceed on over to his tool shed, take his best wood chisel and a hammer, and commence to do strange things...
I remember back in 1964, ...one early morning I was left unsupervised, I went outside and got to dinking around like normal...I got a hold of Gpaws crosscut saw!...It was taller than me! I was intrigued! With nothing better to do, I decided to start on one outside corner of his shop and see if I could cut the whole damn deal in half! Nearly made it too! Even with all the nails! Before some adult came rushing out of the house wondering what all the racket was about!
Another early morning, after a heavy over night ice storm, my old Mans flivver was coated with a layer of ice about an inch thick...So like any good Son, I got a hold of a hammer and commenced to breaking it all off! Like those guys on the crab boats do? I was nearly finished with that project before the adults woke up...Parents shouldnt sleep in or leave tools laying around...
So yeah, my guess is a kid..about 6yrs old...see the nice tight 90 degree quadrants? Firm strikes? Definitely a 6yr old boy of some practice...a 4yr old would be all off on the angles...
I found a few Indian pennies with a similar marking. Could be a counterstamp but im betting yours was just boredom. I dont yave the pics of my Indians but I found the same exact marks on a nickel online. The site said counterstamp. My indians had one hole on each one as well.
I have a cut piece 1/4 of a King George Copper. Early on in New England folks cut them up for change just like they did silver in the south, so a quarter of a cent would be a farthing like in old England. I have also seen a King George II cut in half good for making change if you don't have a half cent handy but an Axe in hand.