I have been implementing the same for older version of GA (Universal Analytics). However, the approach should be the same.
You should setup a utag.link() call using a DOM Ready extension. For example, if we talk specifically about Sign Up then try the following approach:
1. Identify the success and failure scenarios for Sign Up
2. Understand the HTML elements that make up the Sign Up button for finding the correct JQuery selector
3. Make a JQuery onHandler extension with the following:
This can be a good starting point for this. Then, you can figure out how to send them to GA using Data Mapping in your Google Analytics tag.