No one knows for sure that a stock market crash is coming anytime soon. However, there are several unmistakable warning signs that turbulence could lie ahead. Treasury yields are rocking multi-decade highs. Stock valuations are at frothy levels by some metrics.

What should investors do if (and it’s only an if, at this point) a stock market crash really is coming? History’s answer is both simpler and more counterintuitive than you might expect.

Image source: Getty Images. Image source: Getty Images.

The strategy with a perfect track record

There’s one investing strategy that boasts a perfect track record. First, buy a low-cost S&P 500 (^GSPC -1.09%) index fund such as the Vanguard S&P 500 ETF (VOO -1.10%) or the State Street SPDR…