If you’d like to track subscribers and/or segment your list, you can follow these steps to use your own custom value:
1. Open the list you want to track opt-ins for.
2. Click on “Custom Fields”.
3. Click “Create New Custom Field”.
4. Name the field anything you want, and make the Type “Hidden Field”.
5. Final setup of the new Custom Field. Note: You CAN make this global if you want.
6. Click on “Create Subscription/Unsubscription Form”.
7. Select the fields you want, and then click “Generate HTML Code”.
8. Modify the generated code, and look specifically for the hidden field. You can see below that the field type is hidden, and it is a custom field. You can change the value of the field for every page you want to put it on. In this example we just made the value: YourTrackingCode. You would change this for every different page you put this on and want to track for.