I would like to mark a field that I defined with InputField. How can I address the field in the Mark command?

Let's assume that you defined a new field as follows:
InputField (10,1) "Company code" (10,30) "Size=4" "Name=mycc"
You can then either use the field text, i.e. 
Mark [Company code]
or the first position given in the InputField command, i.e.
Mark #[10,1]