Honer derailleurs were manufactured by Max Honer in the town of Spaichingen in Baden-Württemberg in Germany. A company called Max Honer OHG operates in Spaichingen today - but it seems to be in the ventilation and air-conditioning business - perhaps it is a descendant of the same company.
Spaichingen is very close to Rottweil, the town that gave its name to those lovable dogs that are inevitably ‘just trying to be friendly’ as they knock you to the ground and sink their yellowing fangs into your jugular vein.
I know nothing else about Honer except that knowledgeable Germans keep mentioning them as a significant manufacturer of derailleurs in West Germany during the 1950’s. Frank Berto also mentions them and has a picture of a single pulley derailleur. I have seen claims that they first started manufacturing derailleurs in the 1930s, but have no way of knowing whether this is true.