Some fonts suitable for use with computer systems produced the "0" character extra squared at the edges, like a rectangle, plus the "O" character a lot more rounded. A further distinction is made in falsification-hindering typeface as used on German car quantity plates by slitting open the digit 0 https://financefeeds.com/gotbit-ceo-avoids-further-u-s-jail-time-after-market-manipulation-conviction/