Similar to the STI, momentum indicators like the MACD indicate short term (at least) bullishness of the S&P 500. However, the weekly chart does not appear to be as bullish.
Looking back at the Dot Com crash shows using the daily MACD to time the bottom exposes the trader to whipsaws. While the trader using the weekly chart wont be able to catch rock bottom, it provides a more certain entry to ride the primary trend.