i work in the service industry as well. If a server ever circled that tip is not included I would probably be tempted to tip less.
I have done it. I gave the minimum "suggested" tip (I think it was 15%) rather than my usual 20% at Disney.
I know that she probably didn't even realize that she was being given less for the circling that the tip was not included, but it made me feel better.
I still feel that circling that is akin to begging. Tipping is a social and cultural custom, it's not mandatory. If it were mandatory there would be a flat fee service charge added. Disney tried to do this with the dining plan for awhile (including the tip in the price) and many people just thought it made for lazy and rude servers. I've been a waitress and a barista, and I was raised by hairdressers. I know that many workers count on tips to make ends meet. However tipping is a pleasantry that is ruled by etiquette. I have the social responsibility to leave a tip, my server has the social responsibility to provide me prompt, attentive, service with a smile... not to beg.
Can you imagine the uproar it would cause if customers started sitting down at a table and handing the server a card saying "I expect prompt, attentive, service with a smile." Oh my gosh, I think that person would get the worst service ever. If a server is expected to provide service without having to be reminded, customers should not need to be reminded either.