Display sucess and fail message

Question

I have a sign up form and once the user has filled up and the details have already been saved i want to display a sucess alert Validation Summary.

And if user has already entered a log in name that exists that it should show t he danger alert  Validation Summary. (im already doing the check to the database in the background, so if this happens it doesnt save but i just want a message to be displayed to the user)

  

 

Thank you in advance