generally a mark on the piston means put it towards the front of the engine. That specific one is a little large.
If that's the only one it may indicate this piston is not part of the original set?
Back in the day, it was not unusual to replace one piston if there was a problem. I did it myself a couple of times. We usually sourced the piston form the "piston pile" at the local junkyard. We didn't care what it looked like; if it was whole and it fit, we'd use it.