I totally agree odal. And, it is still under the general English category of hallmarks as defined by the dictionary.
If I was to question the validity of the German purity mark I would say the German purity mark is a questionable hallmark because of the lack of government enforcement of the purity standard. There is no basis to deny it is a hallmark.
Of course, if we were speaking German there are a number of different terms we could also use. But, we are not speaking German.
