If they don't change the design, and I paid for the mug, (me - I'm not borrowing my sister's mug or what ever) what is the difference between you buying a mug and staying for 7 days, and me buying a mug for a 3-day stay and coming back to the same resort for a 4-day stay some months later???
Last time I went to a resort on property, I bought TWO mugs, one for me, one for my brother. I am bringing it back, and I told DB to find his and bring it back. (Chances are, his is lost. He will buy another if it is.) Believe me, no WAY did the two of us come close to drinking enough to come out ahead on those mugs....and we tried.....and that is not counting the THOUSANDS of dollars we easily spent otherwise.
Now, you could make a case that it would be wrong for me to give my mug to my sister to take with her when SHE stays at that same resort, and I would agree. You could make a case that it would be wrong for me to buy one mug for me and my brother to share, and I would agree. Also you can't buy a mug at one resort and refill it at another resort or at the park, or bring it back to another resort, and I would agree.
To me, those signs make it clear to people who might not understand the concept that you can enjoy your very expensive mug for more than just today - you don't have to buy one each day that you are there - it is good until you leave, and you can keep filling it up.
Frankly - I'm coming back for the REST of my stay at that on-property hotel. (Having said that, I hope they didn't change the design.)
Maddle