Fading objects out of the document is very common with modern user interfaces. You can always have small popup boxes or notifications which need to display and then hide after a few seconds. Using the fadeToggle function you can quickly hide and display any objects in your DOM. Keep this code handy if you will ever need such functionality in a website interface.
$("a.register").on("click", function(e){
$("#signup").fadeToggle(750, "linear");
});