Every card can hold extra fields of your own. Choose Manage fields, then + Add field, name it, and choose whether it holds text, a number or a date.
Lists such as client types or property statuses can be edited too. Choose Edit list to add an option, rename one, drag options into a new order, or hide one you no longer use and restore it later. When you delete an option that is in use, RemoSign asks which option those records should move to. The option Other always stays last and opens a free text field.