s.mu.Lock()
	defer s.mu.Unlock()

	size := int64(len(s.records))
	h, err := tlog.TreeHash(size, s.hashes)
	if err != nil {
		return nil, err
	}
	text := tlog.FormatTree(tlog.Tree{N: size, Hash: h})
	signer, err := note.NewSigner(s.signer)
	if err != nil {
		return nil, err
	}
	return note.Sign(&note.Note{Text: string(text)}, signer)
}