OnClickedCircleLabel event  
The OnGetCircleLabel event for several series types (Polar, Radar, WindRose, etc) allows replacing the default text used to display labels around the series circle.

For example, append the "c" character to all labels:

procedure TSeriesGetCircleLabelEvent.Series1GetCircleLabel(
  Sender: TCustomPolarSeries; const Angle: Double; Index: Integer;
  var Text: String);
begin
  Text := Text + 'c';
end;