If a joint return is filed, both spouses must sign the return. If your spouse cannot sign because of a medical condition and requests that you sign the return, sign your spouse's name in the proper place followed by the word "by" (your signature), followed by the word "husband" or "wife." Be sure to also sign in the space provided for your signature. In addition, you must attach a statement that includes the form number of the return you are filing, the tax year, the reason your spouse cannot sign the return, and that your spouse has agreed to your signing for him or her. If you are the guardian for your spouse who is mentally incompetent, you may sign the return for your spouse, as guardian. If your spouse cannot sign the return for any other reason, you may sign it only if you are given a valid power of attorney. The document granting you power of attorney should be attached to the return when it is filed. Form 2848 (PDF), Power of Attorney and Declaration of Representative, may be used for this purpose. If you are filing a return for a minor child who cannot sign the return, sign the child's name followed by the word "by," your signature, and your relationship, such as "parent" or "guardian for minor child."