Spiritual sign-offs have always been a pet hate, because they make God sound trite, and the God I know is anything but. If I receive these sorts of "yours in the shed blood of Christ" type messages, I respond in the same way I have since my teenage years, with "Yours in Ept", "Yours in Sect", "Yours in Trepid", "Yours in Solent", or any number of other Dad-joke variants. Amazing how many people I've annoyed this way, and yes it's childish, but I've always found it a good way to snap people out of their spiritual pretentions.