Unknown European car registration number

Hello together, for a few days now a Mercedes-Benz CL or CLS (current model) with the following identification number: white sign (plastic), two letters (centered): CN, square EU flag to the right of it (i.e. blue ground with star wreath). (see picture, where the identification number has no black edge. This should only represent the edge) A country flag is not to be found in/at/under the EU flag or elsewhere. I would really be interested in In another forum I read about a similar but not identical mark (also with the letters CN), but the sign was a normal so-called euro mark. But this is not the case here. Maybe someone can rhyme with it? Best regards, hangglider01