The customer migrated to a new Symantec Management Platform (SMP) server (since he needed to upgrade to a newer version of the OS) and kept using the preexisting database.
Under Manage>Software Catalog or Manage>Software, places like 'All Software Components', he noticed that any custom icon that he added to any of the software components were missing.
ITMS 7.6 or later
Custom icons are saved locally on the SMP server and not moved automatically in case of a migration to a new SMP server. Since the customer migrated to a new server, those icon files were not copied over.
If you still have access to the previous SMP server:
Go to "...\Program Files\Altiris\SoftwareManagement\Web\AppIcons"
Copy the icon files from here into the new SMP server in the same path
Refresh Console and verify that the custom icons are displayed
If you don't have access to the previous SMP server, then you will need to re-import those icons.