These stickers were used on Italian license plates between 1994 and 1998, when the origin code was not shown any more on the plate. They are not ufficial at all and you can easily see from the pictures that they are very different from one another and that they were put on the right, on the left or even in the middle of the plate. Sometimes they show the province of the vehicle, some other times just the "I" for Italy: just to say how different they can be!
