swg_tdr, every executive broker (or the executive part of a broker if they are your prime & executive broker at the same time, as is the case with most of the popular internet accessed brokers) has the duty to keep buyers/sellers anonymous to the markets.
They may also not provide information about the state of a portfolio (which resulted in that strange decision of the trade protocol comities that you CANNOT see the difference between a short sell and a long sell, the prime brokers must manage that 100% and are responsible for it). This what makes it still possible to be long and short at the same time for a same stock (which is illegal) by using two prime brokers.
Hence an electronic community (Market Maker(s)) that receive early access to an order (they are given the opportunity to publish it to their book before NASDAQ publishes it) receive exactly the same information as NASDAQ. That is, the Broker ID is visible, but those brokers have so many transactions for their customers that it would be hard, if not impossible, to single out an individual buyer/seller based on volume/price. The more, broker cut orders in little peace's to more easily pick small amounts from the level stacks.
So, for an MM to put a target on a buyer's/seller's back, that is impossible. However, brokers, that is another story. Just saying :)
AIMO
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