You know, the McDonalds in Menlo Park is probably the most uptight McDonald's I've ever seen. They have three plaques on the wall. The first one explains that they have the right to kick you out the building whenever they want. The other two explain what actions result in getting kicked out.
#1. Customers are allowed only ONE refill per visit.
Maybe there was trouble in the past, where someone would buy a small drink, then spend the next six hours in the building, occasionally refilling the drink as an excuse to stay? I don't know. I can't think of a refill-related situation which was so serious that they had to custom-make a plaque to ensure it never happened again.
Personally, the "one refill per visit" rule bugs me. I don't drink soda at home, so going to a place with soda dispensers is sort of a novel experience for me. I like to try out all the different sodas--or at least the ones I like--by filling up my cup halfway, drinking it, then filling it with another type of soda. This rule ruins my ability to try multiple sodas! It forces me to pick one and stick with it.
#2. Customers may not use the same cup on more than one trip.
In other words, I can't save my plastic cup from last week and use it to get refills this week. Yes, that makes sense, but how did it become such a serious problem that this McDonalds decided they needed to make a plaque, addressing the issue? Was there a customer who has been living on the same plastic McDonalds cup for the past five years or something? There must have been a dastardly criminal called the Serial Refiller, better known as "The Soda Jerk". He burst into the store, filled up with soda, then dashed away before security could check the expiration date on the cup. After he had robbed McDonalds of $54 billion in profits, they decided to take action against him.