Best Practice for displaying an unlimited number?

I am redesigning an interace that uses 0 (zero) as it’s indicator of ‘unlimited number’. For example:

Start at row 3 and continue to row 18 - OK
Start at row 1 and continue to row 94 - OK
Start at row 8 and continue to row 0 < as you can see, the worst indicator you could use to indicate unlimited is 0.

Further constraint: the unlimited number is displayed in a small text box so there isn’t room to spell anything out.

Is anyone aware of a best practice to display an unlimited number indicator besides going old school and typing 999,999?

Thank you.