To prevent attackers from knowing whether an account exists or not your signup must only take an email address and provide no feedback in the UI if the sign up succeeded or not. Instead the user would receive an email saying they’re signed up. The only way an attacker would know if an account exists is if they had access to the target’s email.
The Kobe Bryant workout routine features a hefty mix of track work, basketball skills and weightlifting. His off-season workout has been called the 666 program because he spends 2 hours running, 2 hours on basketball, and 2 hours weightlifting (for a total of 6 hours a day, six times a week, for six months).