Set the user filter on the Company User Page.  (Bottom half of page.)
     This feature allows you to preset the Filter for this user.  By default the filter is set for this user to only view tickets in which they are one or more of the following:  Ticket Creator, Customer, Assign, Location, Bill To or Ship To.  
     You can remove all user names.  This allows this user to view all tickets based on their Security Access Level.
     If one name appears (typically the user); this allows this user to view all tickets for this one name based on their Security Access Level.
     You can add more than one name.  Therefore, all tickets for each name are available to be viewed based on the user Security Access Level.

This is the user filter.  There is also a site filter.  The site filter controls what is displayed based on the User filter.

Hint:  If no name appears under this setting, the user filter is not set.  All tickets will be visible.

Security - Ticket Filter (Which tickets can this user see?)

Name:

This user can see all tickets. Search for a contact to filter their access.

This filter can be used to limit which tickets this user can see. You can search through your contact database and if an ticket is in any way associated with any of the contacts you've selected, the ticket will be visible to this user. All tickets not associated with the contacts you've selected will be hidden from this user. If no contacts are chosen then the filter is empty and all tickets will be visible to this user.