The 2.0 millennials version of Wall Street’s oldest stock market indicator just suffered the so called death cross for the first time in over 2 1/2 years.
What is the oldest stock market indicator? Dow Theory.
How does Dow Theory work?
According to Dow Theory, movements of the Dow Jones Industrial Average (DJIA) have to be confirmed by the Dow Jones Transportation Average (DJTA) and vice versa. Divergences, such as DJIA making a new high without confirmation by DJTA are considered bearish. Dow Theory has been in use since the 1950s.
What is the 2.0 millennials’ version of Dow Theory?
Mobility and transportation have been revolutionized by semiconductors. The PHLX Semiconductor Index (SOX) is often considered the new transportation sector of the 21st century. As such, weakness of the semiconductor sector would be a warning for the millennials’ version of Dow Theory.
What is the death cross?
The death cross appears when the 50-day simple moving average (SMA) drops below the 200-day SMA. This just happened for the PHLX Semiconductor Index. The last time this happened was all the way back on March 17, 2022 (which ended up being a timely warning for the stock market).
In addition to the death cross, the SOX also peaked 5 month prior to the Dow Jones Industrial Average, which constitutes a bearish divergence.
Is the PHLX Semiconductor Index death cross really as menacing for stocks as it sounds?
To find out, we will look at other times when the 50-day SMA for the PHLX Semiconductor Index (SOX) fell below the 200-day SMA (after having been above for at least 1 year). There were 8 prior instances (signal dates).
The orange dots on the chart below highlight all signal dates.
The various graphs of the next chart show the S&P 500 performance for the year following each signal date.
The performance tracker at the bottom shows the average S&P 500 performance for the next 1, 2, 3, 6, 9, 12 months along with the percentage of positive returns. 
The first few month after the signal sports the worst performance (-0.43%) with only 37.5% of the signals being positive. Returns got better thereafter, but remain soft for the entire year.
Conclusion: While the SOX death cross is not an outright sell signal for stocks, it is a warning that more weakness may be ahead.
The SOX itself may be carving out a triangle. A break below support around 4,850 could spark a quick selloff. 
Investors may trade the semiconductor sector with ETFs like the VanEck Semiconductor ETF. The S&P 500 can be traded via ETFs like the SPDR S&P 500 (NYSE:SPY), iShares Core S&P 500 ETF (IVV), or Vanguard S&P 500 ETF (VOO).