Path - Shows a smiley on the pressed state of its signup button.
Trello - When signing up, Trello asks you to confirm your email and gives you a direct link to whichever email service you use.
/via Tyson Gach
Yahoo - Trying to sign up using a future date won’t work
YouTube - If you are not logged in, the “respond to this video” textarea asks you to Sign in or Sign up on mouse-over.
/Via Marian Buhnici