How do I sign the signature block for a decease spouse? In you signature, John Doe filing as decease spouse, then in spouse signature block sign Jane Doe?

You should sign the return and write "filing as surviving spouse" in the signature area below your signature.

Thanks do I leave the spouse signature block blank then?

Yes. If the software didn’t enter this, write “Deceased” and spouse’s name and date of death at the top of the 1040.  A complete answer from the IRS is here:

https://www.irs.gov/faqs/irs-procedures/signing-the-return/signing-the-return