Flash message in redirect not working

I have the following in my controller:

redirect_to signin_path, :notice => "The email is already registered"

In my view I have

<%= flash[:notice] if flash[:notice] %>

But the flash message does not appear.

However if I do the following in the controller

flash[:notice] = "There is already an acount for this email. Please Login to create your board."
redirect_to signin_path

It does work. What is the reason the first one does not work?