There is no data format you can specify that will display 0 in place of a negative.
A calculation field could, however, make such a substitution and then you can put it on your layout in place of the actual data field:
If ( Field < 0 ; 0 ; field )
Max ( field ; 0 )
Or I suppose you could place a 0 as layout text on top of the field and use conditional formatting to hide the 0 when the value is 0 or larger and to hide the data in the field when the value is less than 0...