Answer: thumbprint

AnswerCrossword Clue
THUMBPRINTCrime-scene clue
THUMBPRINTIrrefutable evidence
THUMBPRINTForm of identification
THUMBPRINT"CSI" find
thumbprintA distinctive identifying characteristic
thumbprintAn impression or mark made on a surface by the inner part of the top joint of the thumb, esp. as used for identifying individuals from the unique pattern of whorls and lines
thumbprintan impression made by the thumb