If you're tired of repeating the phrase "add another signature," there's good news: there are plenty of synonyms for this task. You might say "append another signature," "include another signature," "attach another signature," "affix another signature," "adjoin another signature," or "supplement with another signature." Depending on the context, you could also use words like "endorse," "validate," or "authorize" instead of "sign," so you might say "endorse with another signature" or "validate with an additional signature." Whatever phrasing you choose, the meaning is the same: you're adding another signature to a document or agreement.