What signature in mail are you talking about? If you use the built in signatures in the settings, then I assume that you can't send mail at all if the page freezes every time that you try to write an email. When you tap the new email icon, and the window pop up, your signature is already at the bottom of the email screen.
So then you are saying that you cannot send emails correct? And you can restore an iPad without losing a thing, of you do it properly. I have restored several devices a few time and I never lost anything.