Display No Results Found message when record does not exists in database in ASP.Net

Dear Sir, i want if i search UserName 'xdeeeee' that is not exist in database then a label should display saying "Sorry ‘USER NAME’ not found".

plz have a look below picture.

<asp:TextBox ID="SearchByUserName" runat="server"></asp:TextBox>
<asp:Button ID="SearchByTagButton" runat="server" Text="SEARCH" OnClick="SearchByTagButton_Click" /><br />
<br />
<asp:GridView Width="90%" CssClass="gvPatients" ID="gvPatients" runat="server">
</asp:GridView>

protected void SearchByTagButton_Click(object sender, EventArgs e)
{

    String ConnString = ConfigurationManager.ConnectionStrings["dbconnection"].ConnectionString;
    SqlConnection con = new SqlConnection(ConnString);

    con.Open();

    SqlCommand cmd = new SqlCommand("Select * FROM sp_userinformation1 WHERE UserName=@SearchByUserName", con);

    try
    {

        SqlParameter search = new SqlParameter();

        //textfield name where u r typing user name
        search.ParameterName = "@SearchByUserName";
        search.Value = SearchByUserName.Text.Trim();

        cmd.Parameters.Add(search);
        SqlDataReader dr = cmd.ExecuteReader();
        DataTable dt = new DataTable();
        dt.Load(dr);

        gvPatients.DataSource = dt;
        gvPatients.DataBind();
    }
    catch (Exception ex)
    {
        Response.Write(ex.Message);
    }

    finally
    {
        //Connection Object Closed
        con.Close();
    }

}

Regards