He looks at the graffiti on the ground carefully.
The nose and lips are slightly deformed with coins thrown on it. It is perhaps an appreciation of the art by pedestrians. He bends down to remove the outer layer of thick coloured chalk used to draw the picture.
His companion is amazed to see that a different picture emerges in white, and the face is familiar. They now know who is the culprit, and that he has gone this way.
Someone has been kind enough to leave this clue. He wonders what could be the motive of helping them.