If you are a member of the US armed forces and you are stationed outside the US or an injury to your body incapacitates you making it impossible for you to file your tax return, you can have a spouse sign the tax return for you and send it in. If you are stationed outside the country then your spouse should fill out the joint return and then mail the papers to you to sign them. It should be sent to you early enough for you to sign it and return it. If you are sure that this is not possible due to circumstances or the area that you are posted in, then you can file form 2848, a power of attorney for your spouse to act in your place in filing the tax return. The form should be specifically filled out stating that the spouse that remains in the US has the power to act in your place in filing your forms and signing in your place.
If a member of the armed forces has a missing status while posted in a combat zone, their spouse can still file a joint return with their name. This can be done until two years after the combat zone activities cease. This tax return remains valid even if its determined that the taxpayer had passed away earlier. If the taxpayer is unable to sign his tax return due to injury and the spouse has to sign in place of husband/wife who is injured, a statement should accompany the tax return stating the nature of the injury and why the individual couldnt sign their tax return. The place where the signature goes, after the spouse signs in place of the incapacitated husband or wife, it should read the name of the spouse who signed it and their relation to the incapacitated taxpayer.
If you are filing a tax return for a spouse who has passed away that year and you have not remarried, your joint return should have your signature in place of the deceased taxpayer and it should read right next to it "filing as surviving spouse".