If you weren't watching housing stocks diverge with the S&P since 2006, or didn't notice that MBS prices via their credit default swap spreads (MBS insurance rates) were crashing, which made hedge funds like Paulson & Co. billions of dollars (see more ABX Index charts from 2007). Actually, some strategic bond funds and ETFs offered to retirees at Morgan Keegan were filled with CDOs backed by toxic subprime ABS that you could have charted out against the S&P as an ABX alternative! I found a chart of the performance from a Tennessee court case.
Or, if you didn't notice when the largest subprime mortgage lender, New Century Financial, went bankrupt on April 2, 2007... When that Bear Stearns credit hedge fund imploded on July 18, 2007, that was the major catalyst that proved systemic risk officially spread to the so called "smart" leveraged institutional money. Then on August 24, 2007, Bank of America bailed out Countrywide (injected $2 billion), the stock market peaked in October, the collateral call fest began, and Bear Stearns was officially bailed out by the Fed. In this case equities and mortgage credit were diverging for years, but the severity of news flows was also a decent trend to watch against economic data and the S&P.