Do I need a credit card to sign up?

No, you do not need a credit card to sign up. However, if you are on the Self-Hosted plan your service will be temporarily paused if after the fourteen (14) day Free period you do not provide a valid credit card. Your service will resume once you provide a valid credit card.
If you are on the Pay As You Go plan and have not provided a valid credit card, your service will be paused when your monthly usage goes beyond the "FREE" pricing tier.