There are several synonyms for the phrase "sign with", including "accept", "endorse", "join", "commit", "agree to", "pledge", and "authorize". Each of these synonyms implies a slightly different meaning, but all convey the idea of formally agreeing to participate in or support something. "Accept" suggests a more passive involvement, while "endorse" implies a vocal or enthusiastic endorsement of something. "Join" implies becoming a member of a group or organization, while "commit" suggests a more serious, long-term involvement. "Agree to" and "pledge" both suggest a willingness to follow through on a promise, while "authorize" implies giving permission for something to proceed.