There isn’t a way to change the indicator as far as I know.
If cells having annotations (“comments”) should be emphasized more clearly, you could do it by a ConditionalFormat.
To be able to define such a format, you need an “introspective function” telling whether a given cell has an annotation. To allow a user function called by a Calc formula to work with a specific cell, you may pass the three relevant index values returned by SHEET(), ROW() and COLUMN().
Function srcCellhasAnnotation(s As Long, r As Long, c As Long) As Boolean
cell = ThisComponent.Sheets(s-1).getCellByPosition(c-1, r-1)
REM The API uses 0-based indices.
srcCellhasAnnotation = NOT IsNull(cell.Annotation.AnnotationShape)
End Function