If you have an account with TD Ameritrade Singapore, you might have received email from them asking you to update IRS Form W-8BEN, both you and co-owner (if you have) of the account.
If TD Ameritrade Singapore does not receive updated info by December 6, 2019, your account will be subject to trading restrictions and U.S. federal backup withholding. Your account will be restricted to closing transactions only, and you will not be able to open new positions. In addition, TD will convert your Foreign account to a U.S. Taxpayer account after the end of this year. TD's clearing firm will also be required by the U.S. Internal Revenue Service (IRS) to withhold 24% of all interest, dividends, proceeds from options transactions, and sales proceeds until they receive the necessary documentation.
Here, I put up a sample W-8BEN and how to fill up this form.