Once in a while in my change I'll get a dollar with a message written or stamped on it. It beats a message in a bottle I guess, but I don't think it'll catch on with advertisers for a while.
Hmm. Imagine advertising on currency. I wonder how much marketers would be willing to pay for something like that. I'm sure someone would do it. I'd think the main substantive objection would be about potential for counterfeiting.
Maybe nanotechnology would provide a way around that. Imagine images changing on the currency, powered by the heat of your hand. Or have I read too much science fiction lately?
Down a few rungs on the technology/currency/entertainment hierarchy is Where's George. I found out about this one when I got a marked-up dollar bill in my change. Anyway, the idea is that you're supposed to go to the site and enter the serial number of a bill and where you found it. Then you turn it loose and see if anyone reports on it again. Don't hold your breath on that one, but the site claims that $141M worth of currency serial numbers have been recorded, and one particular dollar bill has been found and entered 13 times. If you ever run into a singleton numbered C04549318H, it was in St. Louis on 11/13/02. (You're writing that down, right?)
Other strange things get written on bills. My favorite was one that claimed that my dollar wasn't "real" money, and pointed me to the Constitution for details. There have been many others, but I can't think of any good examples right now.
Of course you can have fun with money just as it comes if you know how to play liar's poker. I learned it on construction sites - at one, the minute there was a break all the steamfitters would whip out their wallets and start playing. Some of them kept special dollars with oddball numbers around to "stack the deck".
So now you know what you can do to entertain yourself on a rainy day. May it never rain that hard.