You sign and efile a return by entering your prior year AGI to verify your identity. If you print and mail your return to file or to give a copy to someone you need to sign it in ink on the signature line at the bottom.
You need your 2018 AGI to efile 2019. The AGI is on 2018 1040 line 7. If you filed a Joint return you use the same AGI for each spouse.
How to find the AGI.
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/01/25947
