Hi,

One way to do that is via a ShapeNode attached to the table; for an example, see the Entities sample project. If you use attached nodes, you will have to filter them out when enumerating diagram.Nodes to process your main nodes.

Another way to implement that is via custom-drawing. Either derive from TableNode and override its DrawLocal method, or handle custom-draw events raised by the Diagram object:

Image lockImage = Image.FromFile("ac0001-16.png");

RectangleF TopRight(TableNode table)
{
	var captionbarHeight = table.CaptionHeight;
	return new RectangleF(
		table.Bounds.Width - captionbarHeight, 0,
		captionbarHeight, captionbarHeight);
}

private void diagram_InitializeNode(object sender, NodeEventArgs e)
{
	var table = e.Node as TableNode;
	if (table != null)
		table.CustomDraw = CustomDraw.Additional2;
}

private void diagram_DrawNode(object sender, DrawNodeEventArgs e)
{
	var table = e.Node as TableNode;
	if (table != null)
	{
		var iconRect = TopRight(table);
		Utilities.DrawImage(e.Graphics,
			lockImage, iconRect, ImageAlign.Center);
	}
}

private void diagram_NodeClicked(object sender, NodeEventArgs e)
{
	var table = e.Node as TableNode;
	if (table != null)
	{
		var iconRect = TopRight(table);
		iconRect.Offset(table.Bounds.Location);
		if (iconRect.Contains(e.MousePosition))
			MessageBox.Show("click");
	}
} 

I hope that helps,
Stoyan