If you want to have some hidden fields in your signup form for segmenting purposes, you're in luck. It's very easy.
- Navigate to the Lists page.
- Click on the list drop down menu and select Signup forms.
- Select the General forms option.
- Make sure you're on the Build It tab.
- Select the field you'd like to hide.
- On the right hand side, under field settings you'll see the individual options for that field.
- Field visibility gives you the option to make a field visible only to you. Select hidden to make the field visible to only you.
- Choose Save Field to save your changes.
This feature is accessible by users with Manager level or higher permissions. Take a look at this article to learn more about the different access levels for a MailChimp account.