23. Signature essential to liability

No person is liable as drawer, indorser, or acceptor of a bill who has not signed it as such:

Provided that —

where a person signs a bill in a trade or assumed name, he is liable thereon as if he had signed it in his own name;

the signature of the name of a firm is equivalent to the signature by the person so signing of the names of all persons liable as partners in that firm.