You sign with  "Your name personal representative for name of deceased".

Suggest that you read IRS Pub 559 (Survivors, Executors, and Administrators) for a lot of good information about filing and signing the final return and estate return and other requirements.

https://www.irs.gov/pub/irs-pdf/p559.pdf

Signature. If a personal representative has been appointed, that person must sign the re-turn. If it is a joint return, the surviving spouse must also sign it. If no personal representative has been appointed, the surviving spouse (on a joint return) signs the return and writes in the signature area “Filing as surviving spouse.” If no personal representative has been appointed and if there is no surviving spouse, the person in charge of the decedent's property must file and sign the return as “personal representative.”

See this TurboTax support FAQ when filing for someone that is deceased - https://ttlc.intuit.com/community/tax-forms/help/forms-you-ll-need-when-filing-a-tax-return-for-someone-who-s-deceased/00/2208438