My Terms is a simple addon that adds a new attribute type to c5. This attribute type can be used to create any number of attributes for use in Signup or Checkout.
When adding the attribute choose Checkbox - My Terms and then enter your terms of service, or anything that a user might need to reference before checking, inside of the attribute content box.
When an end user clicks the link, in the form, it will open a modal popup with the text you entered in the attribute content box.
If you would like to contribute to making this addon better, you can find the public repo here.