If you are using an advanced form integration in Justuno you have two places where you can hide fields after creating the form. This is useful for customers who want to push information to their email marketing application without a customer knowing or having to insert it themselves
You can also use a hidden field to identify the source of the subscriber, i.e. that they came from 'Justuno': see how it's done.
Option 1: Hide the field in the form
Option 2: Hide the field under layers in the design canvas. The eyeball icon will hide the layer
Source: Pass the subscriber's source in a hidden field within the form