Warren Buffett's Favorite Indicator Just Flashed a Major Warning

It is clear stocks are in a massive bubble based on their Price to Sale (P/S valuation).
What about the economy?
Warren Buffett once famously stated that his favorite means of valuing stock was the stock market capitalization to GDP ratio.
Below is a chart for this metric. As you can see, the stock market today is as overvalued relative to the economy as it was at the peak of the 1999 Tech Mania.