First that comes to mind is Adler and Phoenix. It's a bit art deco so I guess 20'-30's but it might have been continued in this shape after the war. Puch and Union (the German one) have used birds and wings also, and there's use of swallows, but this one doesn't look like a swallow.

There has also been a period in German history where nationalistic symbolism was quite popular, and all kinds of nationalistic emblems appeared on the front fenders. And the Eagle (Adler in German) was and still is their national heraldry bird. The german word is Schutzblechemblem, Schutzblechfigur or Schutzblechreiter fur such an item. If it's German the letters probably refer to the location of the manufacterer. I will look if I can find some Phoenix emblems later, Phoenix was a Dutch manufacturer, pretty high end, but not very well documented on the internet.

So you might try google images with those german words, try DuckDuckGo and set location to Germany, and try German E-bay to find a simular one. Or you might show us more pictures of the bike as frame shapes were pretty country specific in those days.