Sorry for your loss.
For 2016 you are allowed to file jointly. When entering your wife's personal information, there is a box to check for "this taxpayer died during this year." Make sure to check it.
In most cases, you are automatically allowed to sign for your wife. However, if there is a will, and probate, and you are not the administrator of her estate, you may need to have the administrator sign for your wife. That would depend on state law.
You may be blocked from e-filing, since the IRS blocks SSNs of deceased taxpayers to prevent fraud. If you try to e-file and get rejected, print your return and mail it in.
If you care for a child dependent in your home, you will also be allowed to file as a "qualifying widower" for the next two years, which gives you the married rate even though you are single.
If your wife had tax-deferred retirement accounts, you have several options on how to handle the money that have different tax consequences. An investment advisor can help or you can post more details here and we can run through the options.
