Radiograph of the hand which reveals an abnormally short 4th metacarpal, as compared to the other metacarpal bones. Although this sign usually is associated with Turner's syndrome, the short 4th "metacarpal sign" carries a short differential diagnosis and is therefore not pathognomonic.
Reference
An evaluation of the metacarpal sign (short fourth metacarpal). Pediatrics 1970 Sep;46(3):468-71.