It is displayed in the issue view on every user field if the selected users are available or not.
Issue View
...
System Fields Assignee and Reporter
...
Custom Fields of Type Single- and Multi-User
Hover User Profile
...
It is displayed in the issue view on every user field if the selected users are available or not.
Issue View
...
System Fields Assignee and Reporter
...
Custom Fields of Type Single- and Multi-User
Hover User Profile
...