Indeed. Ponzi attempted to buy International Reply Coupons in countries where they were cheap, then exchange them for stamps in the US and sell the stamps for much more than the purchase price of the IRC.

Of course, it didn't work. There wasn't anything fundamentally wrong with the arbitrage scheme, but the profit per coupon was way too low to make it feasible as a business. Ponzi pivoted to paying off older investments with new investments, and the rest is history.