What does an asterisk (*) mean when shown beside a field name in the attribute table? I would think those are reserved field names but they are not.
It means that the field is indexed. You can change the character used to indicate whether a field is indexed under the Table Options > Appearance menu:
The asterisk means that the field has an index. A Shapefile does not have any indexed fields by default, you need to add them. A GeoDatabase Featureclass always has a spatial index on the Shape field and attribute index on the ObjectID.