In July of 1933, Newfoundland surcharged 8,000 of its 75c "Labrador, Land of Gold" airmails issued the month before for use on the Chicago to Rome Flight of General Italo Balbo. Scott '13 prices the stamp unused at $325.00 ($500.- for NH).
I recommend purchase of the stamp in VF NH or LH condition, or used on a flight cover. The stamp is of interest to Aviation topicalists, and possibly also to collectors in Italy, as Balbo was a prominent Fascist and Mussolini's heir apparent. I'm unaware of any fake surcharges for this issue, but as with all valuable overprinted stamps, it might be prudent to obtain expertization as a condition of purchase.
Those interested in learning more about investing in stamps are encouraged to read the Philatelic Investment Guide ($5), available on Kindle, and accessible from any computer.