The definition of an additional signature on a document is quite simple – it is the signing of a second name to that document, after its initial signee. This second signature is often used as a form of validation or endorsement by a third party, such as in the case of a legal contract or financial transaction. Whether it is required or not, including an additional signature on a document can provide important protection and reassurance for all involved parties. An additional signature can also serve as a safeguard against any potential disputes that might arise in the future, making it an important part of the official business process.