1a. In insurance, this is an added, special provision to an insurance policy that improves or constrains its coverage. 1b. In other types of contracts, this one or more addenda not part of the original, yet is integral and legal when attached. Also, refer to attachment and rider. 2. In Trading, this is the signing of a legal document in a legal capacity. Signing any negotiable instrument, be it a bill of exchange, bill of lading, delivery order, or other document of title, means the signer (1) guarantees to being the legal owner of the instrument, (2) knows of no defect in it, (3) has received it for value received in good faith, and (4) in the normal course of business, is legally allowed to transfer it to another party. Signing a contract confirms approval of its contents and terms. A third-party signing a promissory note means if the principal borrower defaults the signer guarantees payment.