What are your rules of tipping?

I work at a casino as a slot attendant. I get above minimum wage per hour, plus tips. Tips are shared by all slot attendants in the department. I went to work today and checked to book on how our tips were for the previous week (they are tallied once each week and added to our paycheck every other week). Our tips were on the low side, low enough that we'll be able to tell in our paychecks. There were two other slot attendants in the room with me when I checked the books and we started a conversation about how low they were.

One lady expressed that we should be able to wear something that states "Tips Appreciated/Welcomed". I told her that I think that is solicitation. She stated that at the cage (Customer Service counter) they have small boxes that are labled "Tips" in plain view of the customer. The slot department also has the same small boxes, but ours are hidden in our employee window of the cage and in our slot office. Cage representatives get considerably less tips than we do even with the clearly marked boxes.

Most of our tips come from jackpot winners. It's nearly impossible to know who to expect a tip from. A smaller jackpot winner might tip you $100, while a large jackpot winner might give you zero. I'm sure there are people that have no clue that you can tip the slot attendant, but I'm also equally sure that there are those that know they can, but just refuse.

The same lady then said she has been to several restaurants where the server asked how much she gratuity she would like to add. I asked her if she was using a credit card and she said no. She said she had no money to add to gratuity. I said I thought it was wrong to go to a restaurant without enough money to add as a tip.

My rule is that I tip everyone that does me a service. My hair stylist (when I get it done), servers, bartenders, etc. I tip 15% of my total at for decent service and 20% for fantastic service. It has to be pretty bad for me to tip less than 15%. I've been a server and a bartender and those tips are important, but it's doubly important to provide outstanding service to get that tip.

So what are your rules on tipping? Would you tip the slot attendant if you won a jackpot? Would you go to a restaurant if you had no money to tip?