If you are using the Group Sign-Up "Self-Book" template you have the option of showing visitors to your calendar who has already signed up for your event. Visitors can be shown as having "Accepted", "Declined", or if their response is "Pending". When you turn on "Show Attendees Link" anyone who can access your calendar can see who has signed up for your event. The attendees' link is only available to the Group Sign-Up template and it will show only the names of the people who have signed up. It will not show any personal information (like emails or phone numbers).
To turn this feature on you will first need to create a custom template. Follow the steps in the image below:
Once you've opened the Self-Book template editor you'll need to make sure that you choose "Signup" as the template type. Then you can click on the checkbox next to "Show Attendees Link." See the image below:
Now when you have this feature turned on you and visitors to your calendar can click on the blue "Attendees" link to see who has signed up for your event. See the image below: