Also any recommended sites that track this for the S&P or particular stocks as I cant seem to find any

Though you could easily do the same calculation for a single stock, but by convention and observation it has no meaning.
The signal was designed to work on the broad index, trying to capture the end of the mood of despair around the end of a bear market.

technical analysis.... voodoo perhaps?

Well, as mentioned in the quote up thread: predicting the market reliably isn't possible. That sort of claim would be voodoo.
But divining times of "more likely to be good" and "more likely to be bad" isn't the least bit difficult.

This particular signal was invented about 60 years ago, with the very modest goals of identifying moments that were above-average times to start long term holds.
It has done that extremely well since then, on average. 60 years is a pretty good pile of out-of-sample statistical validation.
What one does with that information, if anything, is up to the observer.

e.g., during months it has been <=4 months since the last "buy" signal, the S&P has risen at a rate of over inflation+20%/year on average since the signal was published.
The overall return from the S&P since that date has been inflation + 6.5%, pretty much spot on the long run average.

Jim