The phrase "signing off on" can be replaced with several synonyms depending on the context of its usage. For example, if it is used in a legal context, "approving" or "certifying" could be used in place of "signing off on." In a business context, "endorsing" or "authorizing" may be more appropriate. In a creative field, "finalizing" or "approving" could work effectively. Additionally, "confirming," "stamping," or "validating" can sometimes be used interchangeably with "signing off on" when referring to giving official approval or authentication. Ultimately, the choice of synonym will depend on the intended meaning and tone of the communication.