foreach(Label l in Controls)    // setting all labels' s visbility  on page to true
     l.Visible =true;

private void SetVisibility<T>(Control parent, bool isVisible)
{
    foreach (Control ctrl in parent.Controls)
    {
        if(ctrl is T)
            ctrl.Visible = isVisible;
        SetVisibility<T>(ctrl, isVisible);
    }
}

SetVisibility<Label>(Page, true);

foreach(Label l in Controls.OfType<Label>())
{
    l.Visible = true;
}

foreach(control l in Controls) {
    if(l is System.Web.UI.WebControls.Label)
        l.Visible = true;
}

foreach(Control l in Controls)
        if (l is Label)    l.Visible =true;

public static void SetAllControls( Type t, Control parent /* can be Page */)
    {
        foreach (Control c in parent.Controls)
        {
            if (c.GetType() == t) c.Visible=true;
            if (c.HasControls())  GetAllControls( t, c);
        }

    }

 SetAllControls( typeof(Label), this);

public void Search(Control control)
    {
        foreach (Control c in control.Controls)
        {
            if (c.Controls.Count > 0)
                Search(c);
            if (c is Label)
                c.Visible = false;
        }
    }

Search(this.Page);