OrphanMarkerRemover

OrphanMarkerRemover, scans the selected index comparing it against the InDesign embedded index markers and displays a list containing the markers that are not present in the index. You have the option to remove the orphaned index marker. 

Orphan Markers only appear after an external index update. If an index entry was removed from the external index the InDesign embedded marker will be left floating in the document with no index entry pointing to it.  Not really a problem, but if you later want to use InDesign to create the index these markers will appear in your index.
Indesign orphan marker marker indexing indesign
You will find Orphan Marker Remover under the extra tools menu.