I will be filing as a "Trader in Securities" for the first time this year and as a result I can use the Schedule C to deduct expenses. But on Schedule C you need to enter a code describing your professional business activity. There isn't an exact description for a Trader, the best I could find was #523900 - "Other financial investment activity." Anyone know what number I should use? Or should I just use #999999, which is the "unclassified" option.