Originally posted by Seanote
When you have ECNs line up in a row on one side or the other (we'll assume the Ask) and there are only MMs on the bid, this is a huge sell signal. If you look at the MMs on the bid all lined up at the same price, they generally will execute 100 shares or so, whatever their obligation is, then almost simultaneously all the MMs will leave the bid and the price will quickly drop.
Speed:
I found this comment interesting since scalpers are often these ECN's all lined up on the offer. I do it myself a lot to get out of positions. If you know it is market makers then I would say it is a sell signal, but often it is just someone trying to get out of their shorts, so it is a buy signal. You can often hit the ecn size, watch the guy panic because he is getting hit and hit cancel and all the offers will disappear for 4-5 cents since a couple guys were all the offers through those levels. Then the sheep high bid, you hit them and get out for a cheap 5 cents. Of course this will depend on what MMs are on the bid. If it is a big guy, you can take your chances, hit the size and play the scenerio I talked about above. If the MMs are pikers then they will bail against the fake scalper size and the scalper will get out as he/she wished. If the MMs are pikers and pull and it goes down because of all the ecn offers, I still look to fade the move long with the sheep who low offers.
I don't know why I am talking strategies on here since we all compete with each other, I just like to talk scalping.