answer:This was originally European, but I’m not sure what year it started. The 40’s, I believe? It was a way to differentiate cars from different countries when they drove abroad. I suspect it was to explain any differences in lights or license plate placement on the car. In later years, it just became a souvenir tag- people from different countries would get them from the country they visited, and put them on their cars. The “fad” appears to have exploded sometime in the 90’s, when places in the US started using them strictly for souvenir purposes.