BTW, I've been in restaurants many times in such instances where the waiter neglects to inform the person picking up the bill that a tip has already been included, knowing that many customers will unknowingly tip an additional 15-20%.
I was at a restaurant once where the waitress wrote "have a good day" over the part of the bill that showed the addition of a required 15% tip. When I saw that, I withdrew anything additional. I hate being conned.