This monument remembers the street musicians of Warsaw. Small bands like this one were very popular before World War 2, and today are hardly to be heard. The monument is in the Praga area, across the river from Old Town. Besides the monument, there is not much to see in Praga (at least not that I could find). But it made for a nice loop in one of my Warsaw runs.
If you have a Polish cell phone, you can SMS to 7141 with the text KAPELA and the tune number (from 1 to 100), and the band will play the tune (the track list is on the drum).