How could I miss this the other day? It’s the textured bit of pavement round the corner from my house which I stand on at least daily waiting for the lights at the pedestrian crossing to change.
Colour this time, and showing the tea-stain shade which adds credence to Dave ‘s surmise as to the formation of these marks. I can’t find any further information about it myself.
I think I missed it (this particular print) because it simply wasn’t there. My guess is that the process (whatever it is) must happen quite quickly given the high levels of wind and pedestrian disturbance on the pavement concerned.