Clicking the icon allows you to set a candidate "Off-Limits" for a specified date range, allowing you options to:
1. Mark a candidate off-limits (no restrictions, just noted).
2. Restrict users from sending them communications BOTH in bulk and individually.
3. Restrict them from being placed on Assignment.
*Please note,
We have a user group privilege which can restrict users from removing the off-limits restriction on a candidate or contact record in Tracker.
With this setting enabled, users can clear this setting and bypass the off-limits. With this disabled, users would be unable to bypass the off-limits set and it would be blank as shown below: