The mm's will buy or sell a stock and the trade doesn't look like other trades.... They buy and sell in small lots to indicate to other mm's what to do.
These are some of their signals. I would suggest getting L2 to help you see the indicators. It's code for mm's to buy/sell with each other without giving it away.
* 100 I need shares. * 200 I need shares badly,but do not take the stock down. * 300 Take the price down so I can load shares * 400 Keep trading it sideways. * 500 Gap the stock. This gap can be either up or down, depending on the direction of the 500 signal.