Marking on Swiss trucks

Can anyone enlighten me please.While on my recent busmans holiday to Italy,I noticed a lot of trucks in Switzerland with a small box in the window,with,(if I recall correctly),what appeared to be an illuminated “h”.
They seemed to have them on varied types of vehicles,ie tilts,tankers,boxes etc.,
Any idea what they`re for please?

It is their version of pay by the km GPS box.

Very good.Thanks Mutley.

mutley75:
It is their version of pay by the km GPS box.

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