[otrs] How to sign answers?

Hi, I have configured otrs to be able to sign in a MIME format. When i compose a new message, I'm able to sign it without any problems. When I want to transfer a message, I still can sign it but unfortunately when I answer to a message, my messages are not signed and I didn't find any way to sign it. Is there a way to do so ? Will it be included in a next release ? Thanks a lot for your answer. Philippe