Many bikes wanting to turn right, get around the traffic stopped at the red light by going up on the sidewalk and then making the turn.
The police stand just around the corner... where they can see the bikes coming... but the bikes do not notice them quickly enough to know not to go up on the sidewalk.
Below these two photos is a quick video showing this...
The video below shows the police pulling over motorbikes for driving on the sidewalk. (Although... once the two of them each have someone pulled over, it's free reign for driving on the sidewalk and not getting caught... I guess it's all about the timing... and your luck for the day if you believe in that kind of thing.)