public void SetDefaultTextSymbol( 
   CIMTextSymbol textSymbol
)

QueuedTask.Run(() =>
{
  //Set a default font. Use its default style
  ApplicationOptions.TextAndGraphicsElementsOptions.SetDefaultFont("tahoma");
  //or specify an explicit style
  ApplicationOptions.TextAndGraphicsElementsOptions.SetDefaultFont("tahoma", "bold");

  //Create symbols
  var ptSymbol2 = SymbolFactory.Instance.ConstructPointSymbol(
    ColorFactory.Instance.RedRGB, 14, SimpleMarkerStyle.Diamond);
  var lineSymbol2 = SymbolFactory.Instance.ConstructLineSymbol(
    ColorFactory.Instance.RedRGB, 2, SimpleLineStyle.Dash);
  var polySymbol2 = SymbolFactory.Instance.ConstructPolygonSymbol(
    ColorFactory.Instance.RedRGB, SimpleFillStyle.DiagonalCross);
  var textSymbol2 = SymbolFactory.Instance.ConstructTextSymbol(
    ColorFactory.Instance.RedRGB, 12);

  //Set default point, line, poly, text graphics element symbols
  ApplicationOptions.TextAndGraphicsElementsOptions.SetDefaultPointSymbol(ptSymbol2);
  ApplicationOptions.TextAndGraphicsElementsOptions.SetDefaultLineSymbol(lineSymbol2);
  ApplicationOptions.TextAndGraphicsElementsOptions.SetDefaultPolygonSymbol(polySymbol2);
  ApplicationOptions.TextAndGraphicsElementsOptions.SetDefaultTextSymbol(textSymbol2);
});