Is your spouse mentally capable of consenting to file a return and just physically unable to sign?
If you e-file, no physical signature is needed, of course, just agreement. If you are filing by mail, this is what the IRS says,
Injury or disease prevents signing.
If your spouse can’t sign because of disease or injury and tells you to sign for them, you can sign your spouse’s name in the proper space on the return followed by the words “By (your name), Spouse.” Be sure to sign in the space provided for your signature. Attach a dated statement, signed by you, to the return. The statement should include the form number of the return you are filing, the tax year, and the reason your spouse can’t sign; it should also state that your spouse has agreed to your signing for them.
However, if your spouse is mentally incapable of understanding and consenting to file a tax return, you have a different problem. You generally need a power of attorney, but a POA can only be granted by someone who is competent. If your spouse has become incompetent and you did not get a POA while they were still competent, you may need to go to a court and get an order declaring you their guardian.
