I refuse to do free ads for anyone except a non-profit org. (FSGW tee shirts for instance), and usual cut off logos on my apparell. I found people in Prague could understand $ quite well. A taxi driver would always figure out where you were from and ask you for the fare at the official rate of exchange. Dollars at the time could be traded on the black market for about 5 times the official exchange rate. I was crossing the famous bridge (whose name I've now fogrotten) with a Russian friend, and we we approached by two men who asked if we wanted to exchange money. My Russian friend looked at me and said (in English) "He means you, they don't want rubles".

Prague joke: Why do Prague policmen always go around in groups of three? One can read and one can write and the other is to keep an eye on those two radicals.