During the filing process (Click File, and start Step 3) in TurboTax you will be asked for either your Original 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.
Note: Once you click File (on the left side of your screen), Steps 1 and 2 have to be completed before you can Start Step 3.