If you have already filed your federal return, please see the TurboTax FAQ below:
How do I e-file my state after I already filed my federal?
During the filing process in TurboTax you will be asked for either your prior year adjusted gross income (AGI) or your prior year PIN. The AGI or the prior year PIN serves as your signature on an e-filed tax return.
For more information, please see the TurboTax FAQ below:
What is my signature ID?