You can configure a post function for a workflow transition to set a sign off step to a specific status. For your selected workflow, select the transition and go to post functions. Add a post function named Sign Off Step Post Function.
You can pick a specific step, or choose to update all steps. The status you select will be set when the post function is applied.
If a sign off step isn’t applicable for a given issue (because the step is only available in certain projects or for certain issue types) the post function will not update that step.