I'll try to answer this if I can. I have always been more of a trader than an investor. We look for stocks with high volume and volatility. MM's make money on trades but they also maintain pools of shares. Remember that when stocks gap up/down the MM must take the opposite side, which is why there is almost always a push in the opposite direction of a gap by 10:30 A.M.

On the pools of shares, traders don't like boring stocks and when volume and range contract the stocks become boring (We have seen this in KRY and the main reason I don't post as much since I am not trading it daily as I did before). For the most part there is always a buyer and a seller, but MM's can sell back and forth to eachother in order to keep an appearance of liquidity. These can sometimes be automated, which is why you might see 100 share trades go off every minute for a while and then a burst of action.

There can be nefarious reasons for trading their own pools such as manipulating the market for a client, but mostly it is the fulfillment of one of their main purposes which is to keep the market liquid and stable. This is mostly seen in low volume markets and in reality the action is probably preventing wide price springs that could hurt the market value for their customers and discourage trading. They want us to trade and they know most retail traders have no clue how the market works. If they don't keep up appearances then nobody trades and the MM makes no money. Don't forget there was a long time when KRY always tarded above 1 million shares and if it didn't we thought it a low volume event. Range was wider too. Now we consider 500k days as high volume.

To further answer your question, MM's have much MORE control in low volume situations. Electronic trades interrupt it but on low volume days there is more MM bid/asks and I think they have 10 seconds to pull the bid/ask after an order comes in so they can avoid a transaction. This is another reason why the price always sits at 3 or 4 decimals but often trades outside of this.

I don't know if there is any "signal" in the trades but I firmly believe they are designed to create an image to keep people interested. I don't think that this is in any way a bad thing for us longs.