This is only available for Tribe community admins.
In Admin Panel> Portal Settings> Messages you can define Moto, Signup rules, Ask rules, Question intro, User intro, Topic intro, and User Terms and Conditions.
- User Terms and Conditions is a message that appears on the sign-up page. By adding a message to this section, a check box will be added to the sign-up page and by clicking on the check box, your members are agreed to your Terms and Conditions (T&Cs). You can put a message like "By clicking on the check box, you are agreed to our T&Cs). You can attach a link of your T&Cs page to the message as well, so users can click on it and read it before clicking on the check box.