I forgot to bring my camera on this trip, but I do have my Treo 650. It's useless as a cell phone here in Europe, but it takes a decent picture in a pinch.
I suspect Heidelberg is one of the few places one might see something like this. These were well-dressed musicians who I suspect are also professional performers judging by their sound. And yes, they were accepting tips in the violin case. I thought they sounded good enough to merit a couple of Euros.