An icon identifier which must be registered through the :php:`\TYPO3\CMS\Core\Imaging\IconRegistry`.
This icon will be shown within the - :ref:`"Inspector [CollectionElementHeaderEditor]"<prototypes.prototypeIdentifier.formelementsdefinition.formelementtypeidentifier.formeditor.editors.*.collectionelementheadereditor>` if the finisher is selected.