Implied pollution from car idling

The sign we have here is a brand new¹ sign located in Espoo, Finland. It forbids idling your car, i.e. having the engine running while the car is parked. The pictorial component of the sign is quite straightforward, with a smoking exhaust pipe of a car being "slashed over" by a the classical red circle slash sign. But I do note that even though it is the behavior of the car (or its driver) that we are restricting here, the red "NO"symbol is mostly positioned over the exhaust fumes arising from the car. Indeed, only less than half of the car itself is visible here, while the gas plume takes up a considerable portion of the pictorial sign.

We suppose that this is to shift the implied meaning of the sign from "cars and people driving them are bad" to "we want to limit the exhaust fumes of your car". In the setting of dog signs, Laihonen & Halonen make a particular distinction between restricting the existing of dogs, versus signaling the impurity of dogs (and their excrements in particular). I see a parallel in here where we do want the restrict cars themselves but their "excrements".

Worthy of note in the analysis of this sign is that it is located on a parking lot that has a large apartment building on one side, and a multipurpose medical/hobby/etc center on the other. So this parking lot might see a lot of cars who are waiting to pick someone up on the one hand, while being situated near aparment balconies.