Google "market maker signals 911" and you will find it states that 911 in MM speak means incoming news.
100 > I need shares 200 > I need shares badly but dont take it down to get em 300 > Take the price down to get shares.... 400 > Trade it sideways based on Supply and Demand 500 > Gap one way or the other, usually to the direction of the 500 trade. Sometimes -if in the middle -keep the price right where it is 911 > News incoming