It's all electronic, if you need to send in a paper copy sign into your Turbo Tax account and print a copy of your return, or hopefully you save a PDF copy and just print that out.
If you are filing by mail you look for the heavy black words SIGN HERE near the bottom of form 1040 to sign and date the tax return. As mentioned earlier--if you are e-filing it is all electronic and you do not need to mail anything.
On the second page of your form 1040, at the bottom, there is a section marked Sign Here. You sign and date there.
If it is a joint return, both spouses have to sign in the order listed on the return.
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