The forwarding script will clip your .signature (assuming your mailer does the Right Thing and puts "-- " on a line by itself before it!) and strip excess whitespace. However, it does limit the message to 180 characters, which last I checked was the limit Verizon imposes.
Your Reply-To: header (or From:, if you don't set Reply-To:) is passed as the sender, so I can reply to you directly from the phone.