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.