It's very common practice to show and success or error message based on different event like Edit, Delete or Notice. In admin theme we can register notification to display.
Success Message:
App::Module('Notification')->Push("Updated successfully.");
Error Message:
App::Module('Notification')->Push("Sorry! Email already exists.","Error");
Warning:
App::Module('Notification')->Push("Password will expire after 5days.","Warning");
Warning:
App::Module('Notification')->Push("No data found.","Warning");