The Shift Sign-up List can be printed either from the Shifts tab of Maintain Events
or from the Troop Calendar detail page.
In either case, you'll see a button Print Shift Signup List that will produce a report like the one shown below.
It shows all of the shifts scheduled for this event, and for those shifts where members have signed up it lists those members.
This makes it easy to see the shifts that still need to be filled.