Renfrew of the Royal Mounted (1937)

Counterfeit bills are being printed in Canada and shipped across the border hidden in blocks of ice. When the counterfeiters force engraver Bronson to make a new plate, he inscribes a tiny help message on it. Renfrew catches a henchman who has one of the new bills. A magnifying glass lets him read the message and he heads out alone to round up the counterfeiters.