If you e-filed your tax return, the 2018 AGI you entered is your electronic signature. There is no physical signature on an e-filed tax return.
If you need a signed copy of your 2019 tax return, print a copy of the Form 1040 and sign the tax return on page 2 of the form.
To access your current or prior year online tax returns sign onto the TurboTax website with the userID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on Download/print return (PDF)
When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state.
This will take you back to the 2019 online tax return.
Click on Tax Tools on the left side of the online program screen. Then click on Print Center. Then click on Print, save or preview this year's return. Choose the option Include government and TurboTax worksheets
If you need a signed copy, then print it and use a pen to sign on the line that says "Sign here." When you prepare your return using the software and you e-file it, there is no physical signature--you "sign" it by entering a PIN or your 2018 AGI. If a lender, etc. wants a signed copy for some reason, then you sign it in ink yourself.