The following is from the Leupold website.
Leupold® is issuing a customer alert to purchasers of products, particularly via Internet sales, in regards to bogus Leupold products that are apparently being illegally imported from the People’s Republic of China. These products bear many of the marks and trade dress of current Leupold & Stevens riflescopes making them very hard to distinguish externally from authentic Leupold products.
In recent months, counterfeited Leupold Mark 4® riflescopes have begun to arrive with increasing regularity at the firm’s Beaverton, Oregon, headquarters for service. These products are not manufactured by Leupold and are not covered by the Leupold Full Lifetime Guarantee.
Leupold employs serial number tracking for all its riflescopes, so if a customer finds a scope that is suspect, he or she can simply write down the serial number and call 1-800-LEUPOLD to confirm if it is indeed authentic.
In general, most of the scopes appear to originate from Hong Kong (People’s Republic of China), and have “Leupold Mark 4” laser engraved on the bottom of the turret in a silver etch, while the black ring on the objective is etched in white and does not include the name “Leupold.” An authentic Mark 4 riflescope will always be engraved black on black and have the name “Leupold” engraved on the black ring.