With exchange back to normal…
.. or misselling of 5% City of Warsaw 1921 Development Loan bonds to gullible US investors.
Speculative investment in 5% City of Warsaw 1921 Development Loan bonds denominated in depreciated polish marks was supposed to generate hefty profits “with exchange back to normal”. But it was obvious at that time that’s not going to happen so I’d say that by today’s standards it was a scam disguised as legitimate, although speculative investment opportunity.