Mysterious Steps in Stockholm

Have you seen these footsteps in Stockholm?

I first discovered these mysterious footsteps outside my apartment almost a month ago. Then they were on the cobblestones down the street from my office. The ones pictured above appeared by the tunnelbana (metro) station in my neighborhood. And now they're all over Stockholm - coming from the lake, across bike paths, along sidewalks. 


My question is: why? And where did they come from? 


Perhaps building anticipation for some major event on the horizon? Or supporting the local AIK football team, whose colors are black and yellow? Trying to make a statement of sorts? Or is someone just bored?


Any info, please share tack!