My comment was in response to a question asking for proof the coupon was signed, but to be sure, I've found it does make a difference. The OP of this thread notes he signed the coupon several times, but had no proof. The auditor's coupon provides some proof as there's probably no way to get that without going to the airport to sign the "bluey". It contains the ticket number for the itin to be upgraded along with the sponsoring person's MP number, name and signature. It's better than a gift letter IME and has certainly worked for those I've sponsored when the agent did not enter the appropriate info, which, unfortunately, seems to be most always.