I didn't know of them until after I had moved to Hamburg, where there are quite a few. My SO showed them to me and told me the background. I was flabbergasted.

I didn't know of them until after I had moved to Hamburg, where there are quite a few. My SO showed them to me and told me the background. I was flabbergasted. Being very interested in history, having studied history at university and never before having heard of them was quite frankly disconcerting for me back then. Since I nearly always stumble (as intended) as it is a visual pattern I now instantly recognize.