The DGT can fine you up to 200 euros for having this sticker on your car.

In Spain, it's common to see vehicles on the roads with various stickers on the bodywork or on the front or rear windows. Classic stickers, from the Vehicle Inspection , environmental regulations, football teams, or the place of origin, among others, are some of the favorites among the population, who choose to decorate their cars with these stickers. But... Are they all legal?
The General Traffic Regulations , in this case, make it quite clear. They do not expressly prohibit the use of stickers, but they do require that they not obstruct drivers' visibility, as they could cause an accident or other hazards on the road.
What does the Regulation say?The General Traffic Regulations, in its article 19.1 , ensure that the driver must have "visibility without interference from films or stickers" under any circumstances: "The vehicle's glass surface must, in all cases, allow the driver clear visibility over the entire road on which they are traveling, without interference from films or stickers."
On the other hand, it also explains that the only "mandatory stickers" that must be placed on the windshield are the stickers from the Technical Vehicle Inspection, that is, the ITV, and the environmental badge from the General Directorate of Traffic , which indicate, on the one hand, that everything is 'ok' for free circulation of the vehicle and, on the other, that it can access the Low Emission Zones without any problem by strictly complying with the established requirements.
What is the fine?If officers believe the stickers on a vehicle in question obstruct the driver's visibility, they can logically be fined 200 euros. This is only valid, as we've indicated, provided the driver's vision doesn't obscure the entire visible area of the road.
Is there a penalty for decorative stickers? We've often seen a sticker that says "Caution, baby on board," a specific place in Spain, such as the Índalo symbol , which represents Almería, or a red and yellow target. Drivers shouldn't have any problems as long as they comply with the requirements and don't harm or endanger their lives or the lives of other drivers.
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