Some fonts created for use with personal computers designed the "0" character extra squared at the perimeters, like a rectangle, as well as "O" character much more rounded. An extra difference is built in falsification-hindering typeface as used on German car range plates by slitting open the digit 0 https://financefeeds.com/clearstream-to-serve-as-a-triparty-agent-for-euronext-clearing/