Is the Surname field an editable field?
It may be easier to use a conditional format expression on the surname field to change the text color, fill color and/or text style as your indicator instead of appending the asterisk should this be an editable field.
The following auto-enter calculation, however will append an asterisk if "TheField" is not empty.
Let ( Sname = If ( right ( self ; 1 ) = "*" ; Left ( self ; Length ( self ) - 1 ) ; self ) ; //remove the asterisk if it was appended earlier
If ( IsEmpty ( TheField ) ; Self ; Self & "*" )
Make sure to clear the "do not replace existing contents..." check box for this field.
Thank you. In the end I took you suggestion of conditional format on the field to change its colur. Managed to get the asterisk addition working, but it was not live, you had to visit the field, however the conditional format is "live" and does the job. Thanks again.