The Federal Reserve's Industrial Production index for the manufacturing sector (FRED: IPMAN). Measures real output of US manufacturers, indexed to 2017=100. This is a volume measure, not the ISM Manufacturing PMI survey.
Tracks the real output of US factories month by month. Sustained declines signal manufacturing recession. One of the most reliable leading indicators of broader economic weakness.
Index baseline is 100 in 2017. Values above 100 = above 2017 output level. Watch the direction and rate of change, not the absolute level. Year-over-year decline below -2% historically signals recession.