From the link:
It is nearly impossible to call a market top before it becomes obvious it has already happened, but the housing stocks have come closest in the past to doing it.
Which is why I keep an eye on LEN, KBH, DHI, MDC, NVR, TOL, PHM AND TOL. If is all not quite well with the market (and the economy for that matter), they are often the first to show the strain.
For the discussion, historical links and the charts: