Do you have developer access to the solution?
Can you get access to the layout with signature required in layout mode?
If so, check the data formatting on that date field.
As a point of interest, if the file was created on a machine that was set to the US date format, then every time a date is cast as text it will be in that format. For example:
Field FlightDate will display as 20/3/2016
Field FlightNumberAndDate defined as:
& ": "
will display as JL165: 3/20/2016 if the file was originally created on a machine set to the US date format.
This may well not be what is happening in your case - from the layout it seems unlikely that the field would be anything other than a simple date field - but if it is there are 2 solutions:
1) Save a clone of the file on a machine formatted to Aus dates and import the data from the original file into the clone
2) Manually cast dates as text, using a custom function if you have FileMaker Pro Advanced.
So FlightNumberAndDate becomes:
& ": "
& Day ( FlightDate )
& Month ( FlightDate )
& Year ( FlightDate )
The first option is preferred but not always practical.