C#”+"；签名窗口属性

我有类AppForm继承的Form，属性为AppIconForm（class）。我希望在设计时在属性窗口中的编辑IconForm属性上显示"+"号，并显示子属性（CloseIcon和MaximizedIcon）。谢谢！：）

public partial class AppForm : Form
{
    AppIconForm iconform = new AppIconForm();
    public AppForm()
    {
        InitializeComponent();
    }
    public AppIconForm IconForm
    {
        get { return iconform; }
        set { iconform = value; }
    }
}
//the code of AppIconForm class
public class AppIconForm
{
    Icon closeicon;
    Icon maximizeicon;
    public Icon CloseIcon
    {
        get { return closeicon; }
        set { closeicon = value; }
    }
    public Icon MaximizeIcon
    {
        get { return maximizeicon; }
        set { maximizeicon = value; }
    }
}

[Browsable]
public Icon CloseIcon
{
  get { return closeicon; }
  set { closeicon = value; }
}