You are only responsible for and can sign the tax return you prepared. 

They are probably doing this because they cant pull IRS transcripts to verify income, thats none of your concern though, dont let them bully you.

Give them the Form 9325 showing that the return has been filed and accepted, along with the return that youve put your name to as paid preparer.

Im sure if you call your E&O insurance company they will advise against you signing anything like that.