Many years ago, I remember that several tourists in Florida were attacked by thugs specialized in tourists. They would crash their car into the tourist's car to make them stop and then, pull a gun. Some victims got killed. Nowadays, rental cars in Florida are not marked as such and cannot be differentiated from normal cars.
I do not expect this level of violence in the countries I rent cars, mainly Germany, Belgium and Spain. However, I know some cases in Spain from the newspapers where thugs targeted tourists specifically. Mostly the loss was only monetary, but even then, that could ruin any trip.
I was told that in Germany, you can recognize a rental through the license plates.
I know that in Spain some rentals, specialize from no-name car rentals, put a sticker on their car, always on the rear, mostly in bright colors like yellow.
In the German case, I assume there's no way of covering the evidence that you are driving a rental.
However in Spain, would that be feasible to cover the sticker with something that could be later removed, some kind of non-permanent sticker? Removing their sticker might damage the paint, and I could incur in hefty costs.
Is that a good idea, or I'm just being paranoid?