public class BootstrapPage : Page
{
    public enum WarningType
    {
        Success,
        Info,
        Warning,
        Danger
    }

    public void ShowNotification(string message, WarningType type)
    {
        var mainContentHolder = Master.FindControl("MainContentPlaceHolder") as ContentPlaceHolder;
        Panel notificationPanel = new Panel();
        {
            LiteralControl closeButton = new LiteralControl();
            closeButton.Text = "<a href="#" class="close" data-dismiss="alert" aria-label="close">&times;</a>";

            Label notificationMessage = new Label() { Text = message };

            notificationPanel.Controls.Add(closeButton);
            notificationPanel.Controls.Add(notificationMessage);
        }
        notificationPanel.CssClass = string.Format("alert alert-{0} alert-dismissable", type.ToString().ToLower());
        notificationPanel.Attributes.Add("role", "alert");

        mainContentHolder.Controls.AddAt(0, notificationPanel);
    }
}

<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Site.master.cs" Inherits="DeceasedSystem.Site" %>

var mainContentHolder = Master.FindControl("MainContentPlaceHolder") as ContentPlaceHolder;