The phrase "sign on" can have various synonyms that convey similar meanings. Some common alternatives include "register," "enroll," "sign up," "join," "apply," and "commit." "Register" suggests a formal, official process of recording information, whereas "enroll" implies joining a specific institution or program. "Sign up" and "join" both denote taking an active role in a particular group or undertaking. "Apply" is often used in the context of seeking employment or membership, while "commit" suggests a more serious and long-term commitment to a cause or organization. Overall, these synonyms demonstrate the different shades of meaning conveyed by "sign on" and offer a range of options for expressing similar ideas in writing or speech.