The answer is: The author highlights a woman’s inability to borrow money without a man’s signature.
To be able to borrow some money from the bank, the character Nora needed a man to sign the papers for her. Since she couldn't let her husband know about it, she seems to have forged her father's signature to receive the loan.
Context:
The conversation in this excerpt reveals a plot complication in the story. Nora borrowed money from the bank without her husband's knowledge of the fact. She had needed the money to take her husband to Italy when he was sick. Nora lied to him, telling him she had gotten the money from her father.
Krogstad works at the bank with Nora's husband and is about to be fired. He blackmails Nora, as we can read in the excerpt, so that she will help him keep his job.