Here It Is
A good Samaritan will always restore money to its proper owner. A good Samaritan would be considerably more inclined to keep it. And this one, with a sense of humor, will at least inform the original owner that their money is gone for good. That said, this is most likely another joke done by someone looking for anything amusing to do with a rubber band, and he certainly succeeded.
Signception
What we want to know about humorous signs like these is: how does the person who made it get any enjoyment out of it? How can they know it made anyone laugh unless they’re continually monitoring it? Perhaps it will suffice for them to know that they have posted the sign somewhere visible. And, to be honest, it’s a really interesting one to look at. At the very least, they were proficient in Photoshop.