yellow townsigns with black letter using the DIN 1451 font:
invented 1920's
tested 1925
introduced 1926 in Prussia
other states followed soon
Picture taken from StVO 1937
Before judging something to be plain wrong you should do your research and resign trying to judge the difference between yellow and white from a black and white photograph.
But you got right that back then it was not called Hürtgenwald, this term did not exist at that time. Americans introduced the term "hurtgen forest" in WW2. Only after the war the Germans adopted it and combined several villages to the municipality Hürtgenwald.