Contacts filter for those not on a mailing list
Within contacts you can filter in various manners but cannot filter those that are not on a mailing list so that you can allocate accordingly, or mailing list specific. Those not on a mailing list may have signed up via the 'sign up page' in Connections but you will have no idea who has signed up. So suggested filter options in Contacts:
Contacts not on a mailing list.
New contacts, added within last 30 days.
Mailing list specific.
Plus notification by email of new sign ups (an option to turn this off should be included as some might receive excessive notifications)