The US Treasury 10-year minus 2-year spread — the classic recession signal, live from FRED.
The spread is the 10-year Treasury yield minus the 2-year. When it is positive the curve is normal; when it turns negative the curve is 'inverted'.
An inverted 10Y–2Y has preceded every US recession of the last half-century, usually by 6–18 months, which is why markets watch it so closely. Source: FRED (DGS10, DGS2).