This is used to track how a signup has been made.
The following options are available:
Visited signup page URL: a user views the signup complete page. e.g. the user is redirected to "/signup/done/"
Redirect from signup URL to signup complete URL: a user is redirected from the signup page to a specific URL (that may not be unique to the signup process) e.g. the user is redirected from "/signup" to their user page "/catlady".