[DefaultValue(null)]
[SRCategory(ReportStringId.CatAppearance)]
public string WatermarkId { get; set; }

<SRCategory(ReportStringId.CatAppearance)>
<DefaultValue(Nothing)>
Public Property WatermarkId As String

using DevExpress.Drawing;
using DevExpress.XtraPrinting.Drawing;
using DevExpress.XtraReports.UI;
// ...
XtraReportCategories report = new XtraReportCategories();
  report.Watermarks.Add(CreateTextWatermark("First Watermark","Watermark1"));
  report.Watermarks.Add(CreateTextWatermark("Second Watermark", "Watermark2"));
  report.WatermarkId = "Watermark2";
  report.ShowRibbonPreviewDialog();
  // ...

private XRWatermark CreateTextWatermark(string text, string id) {
XRWatermark textWatermark = new XRWatermark();
textWatermark.Text = text;
textWatermark.Id = id; 
textWatermark.TextDirection = DirectionMode.ForwardDiagonal;
textWatermark.Font = new DXFont("Verdana", 36);
textWatermark.TextPosition = WatermarkPosition.InFront;
textWatermark.ForeColor = Color.Red;
return textWatermark;
}

Imports DevExpress.Drawing
Imports DevExpress.XtraPrinting.Drawing
Imports DevExpress.XtraReports.UI
' ...
Partial Public Class Form1
    Inherits Form

        Public Sub New()
            InitializeComponent()
            Dim report As New XtraReportCategories()
                report.Watermarks.Add(CreateTextWatermark("First Watermark","Watermark1"))
                report.Watermarks.Add(CreateTextWatermark("Second Watermark", "Watermark2"))
                report.WatermarkId = "Watermark2"
                report.ShowRibbonPreviewDialog()
        End Sub
    ' ...
        Private Function CreateTextWatermark(ByVal text As String, ByVal id As String) As XRWatermark
            Dim textWatermark As New XRWatermark()
            textWatermark.Text = text
            textWatermark.Id = id
            textWatermark.TextDirection = DirectionMode.ForwardDiagonal
            textWatermark.Font = New DXFont("Verdana", 36)
            textWatermark.TextPosition = WatermarkPosition.InFront
            textWatermark.ForeColor = Color.Red
            Return textWatermark
        End Function
End Class

using DevExpress.XtraReports.UI;
// ...
public partial class XtraReport : DevExpress.XtraReports.UI.XtraReport {
   private void XtraReport_BeforePrint(object sender, System.ComponentModel.CancelEventArgs e){
            XtraReport report = new XtraReport();
            ExpressionBinding watermarksBinding = new ExpressionBinding();
            watermarksBinding.EventName = nameof(BeforePrint);
            // Specify an expression that is rendered within the BeforePrint event.
            watermarksBinding.Expression = "`Iif([Arguments.PageIndex]=0,'Watermark_0',Iif([Arguments.PageIndex]%2=0,'Watermark_1','Watermark_2'))`";
            watermarksBinding.PropertyName = nameof(WatermarkId);
            report.ExpressionBindings.Add(watermarksBinding);
    }
}

Imports DevExpress.XtraReports.UI
' ...
Partial Public Class XtraReportCategories
    Inherits DevExpress.XtraReports.UI.XtraReport

   Private Sub XtraReport_BeforePrint(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs)
            Dim report As New XtraReport()
            Dim watermarksBinding As New ExpressionBinding()
            watermarksBinding.EventName = NameOf(BeforePrint)
            ' Specify an expression that is rendered within the BeforePrint event.
            watermarksBinding.Expression = "`Iif([Arguments.PageIndex]=0,'Watermark_0',Iif([Arguments.PageIndex]%2=0,'Watermark_1','Watermark_2'))`"
            watermarksBinding.PropertyName = NameOf(WatermarkId)
            report.ExpressionBindings.Add(watermarksBinding)
   End Sub
End Class