MapPoint pt = new MapPoint(X, Y);
ESRI.ArcGIS.Client.Graphic graphic = new ESRI.ArcGIS.Client.Graphic();
TextSymbol sym = new TextSymbol();
sym.Text = "Text goes here";
sym.FontSize = 9;
sym.Foreground = new SolidColorBrush { Color = Colors.Black };
sym.OffsetX = 2; // experiment with offsets to help horizontally
sym.OffsetY = 2; // and vertically
graphic.Geometry = pt;
graphic.Symbol = sym;