BigPanda has the functionality of assigning an incident to a specific user. When an incident is assigned, the property "assignee" is set with the email address of the user assigned to the incident.
Here three useful tips on using the property "assignee":
1. Search for incidents assigned to a specific user
assignee = firstname.lastname@example.org
2. Search for incidents that have been assigned
assignee = *
3. Search for incidents that have not been assigned
assignee != *