I think this strategy is relative. Meaning that you need to compare the current day action with the previous days action. Say you get big blocks of buying today on a specific stock (over 50K,80k, or even 100K$!!). And you compare that to the average daily action on the stock..If you see a big discrepency there's a big chance that the stock is about to move (i.e. insiders know something). Again, this technique is not guaranteee...
TARR is a great example showing that reading the TAPE could have been a sign to buy before the news..Another example is DPHIQ on the dip day to 47 cents..someone bought a block of 2 million shares @ 50 cents..clear indication of a reversal...