Jim Amormino, spokesman for the Orange County Sheriff's Department, said the victim was in his car after picking up the valuables from Saatchi Jewelry when three men in a car boxed him in.
The men smashed the front passenger window, slashed the tire and stabbed the courier in the arm and hand before grabbing a bag containing a Rolex watch, cash, jewelry and the coins, all worth about $50,000.
They then got away in a car driven by a third man.
"Like five minutes later he came back with stab wounds and blood on his arm" said Farid Saatchi, the store owner. "He was very calm."
Two of the suspects were described as Black, about 25 to 27 years old. All three suspects were between 5-foot-6 and 5-foot-7, about 150 pounds.
The Associated Press contributed to this report.