Section 20. Liability of person signing as agent, and so forth.- Where the instrument contains or a person adds to his signature words indicating that he signs for or on behalf of a principal, or in a representative capacity, he is not liable on the instrument if he was duly authorized; but the mere addition of words describing him as an agent, or as filling a representative character, without disclosing his"principal, does not exempt him from personal liability.
No liability when: 1. Duly authorized 2. Adds words to his signature indicating that he signs as an agent 3. He discloses his principal