To be tested with supported browsers and IE8 (or Opera) for PNG fallback.
Note: both icons are the same, but have different file names.
Check the icon 'Assign roles' in blocks when editing mode
Check the icon 'Assign roles' in the navigation block (Course admin > Users > Enrolled users)
Check the icon 'Enrol users' in the navigation block (Course admin > Users > Other users)
Check the icon 'Enrol users' in the course list page (Home ► Courses ► Miscellaneous ► Add/edit courses)