I recently did some research on this myself and can offer some (non-expert) information.
The IRS has fairly stringent and specific rules about what a person has to do to have a "business" of trading.
It is not normal for an individual who invests to be considered a business. An individual must really prove that they are in the business of trading stocks.
This may include having a separate corporate structure and separate finances from your personal money and keeping your trading account in the name of your corporate entity.
The other side of this coin, is that if you are a successful independent trader, then usually setting up a corporation or LLC will save you a lot in taxes. There are even specific Accounting firms who specialize in doing taxes for individual traders.
There are links at the hub below which lead to more information on this subject, which I gathered as part of my research.