Function signed 

pub fn signed() -> FnOptionArg

GPG-sign the push request to update refs on the receiving side, to allow it to be checked by the hooks and/or be logged. If false or –no-signed, no signing will be attempted. If true or –signed, the push will fail if the server does not support signed pushes. If set to if-asked, sign if and only if the server supports signed pushes. The push will also fail if the actual call to gpg –sign fails. See git-receive-pack(1) for the details on the receiving end. –signed