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My approach to verification: look up a few famous "Schriftenmaler" and see what they are called. Examples: Rudolf Koch, Kaufmann. Then, look up "Letterer" AND "Type" (to limit the number of hits to meaningful hits).
In Rookledge's International Directory of Type Designers, the expression "Lettering artist" is used, but that would be leaning towards type design, while "Letterer" is more general, as is "Schriftenmaler".