No, users do not need to sign in / register to post to a Kudoboard. If you'd prefer to not create an account and stay anonymous you're welcome to choose "Skip Email" and add as a guest.
The only exception is when users are posting to boards created through Business & Enterprise plans; in this case, they are required by default to register before posting as an added security measure for you. Please note that this requirement can be removed by request. Simply reach out to us at firstname.lastname@example.org.