(1) Where a person signs a bill as drawer, indorser, or acceptor, and adds words to his signature, indicating that he signs for or on behalf of a principal, or in a representative character, he is not personally liable thereon; but the mere addition to his signature of words describing him as an agent, or as filling a representative character, does not exempt him from personal liability.
(2) In determining whether a signature on a bill is that of the principal or that of the agent by whose hand it is written, the construction most favourable to the validity of the instrument shall be adopted.