Is it allowed? Köln vs Düsseldorf

I see this ad and my first reaction is: Can they do that? This is an advert for Kölch, the Köln - Cologne - beer, and as I have mentioned before, Köln and Bonn has a long history of conflict and competition. I am not sure what it's about but Düsseldorf is the capital of this state while Köln is the bigger city, I assume that's part of the problem, but I have the feeling that it's much deeper than so.

Personally I love both cities, they both have a great selection of things to do and concerts, restaurants and so forth. But I seem to only get away with it because I am a foreigner...

Both cities have their special local beer as well, in Köln (Cologne) it is Kölch and in Düsseldorf, some 50 km away it is Altbier, a darker one. You don't find Alt in Cologne and you don't Kölch in Düsseldorf - except for one place, the only exception I know of, a Cologne bar down in Medienhafen, Düsseldorf, Eigelstein. But that really is the exception - I once asked for Kölch in the Düsseldorf airport, long before I lived here, and that truly upset the guy at the counter. Ouch! Won't do that again...

So when I saw the sign below I was really surprised. It's brave to advertise Kölch here. And then I remembered that I'm not in Düsseldorf... :-)