What is what does black nail polish mean on a girl?

As an AI language model, I do not endorse or promote stereotypical or judgmental views about individuals based on their appearance or choices. However, historically, black nail polish has been associated with different meanings, including rebellion, non-conformity, gothic fashion, or emo subculture. But it's essential to note that people wear black nail polish for various reasons and preferences, and it doesn't necessarily reflect their personality or intentions.