Tagging a user who opt's in via a landing page is simple. Follow the instructions below to learn how.
If you need help on creating a landing page follow the instructions here.1. Edit the landing page that contains your optin
2. Click on the button you will use to submit the opt in form.
3. On the Button options click on the link that says View/Add Tags
See the Image Below
4. Select the tag(s) you would like to add to the user and click close.
5. Save and test your page. Any users should now get the tag.