Grey products are imported through unauthorised channels, meaning they risk not being covered by the manufacturer's warranty and may even be second-hand or stolen, warns Tamron.
Removing the original serial number is designed to hide the source of products that have not been sold via an official distributor.
Though UK consumers have not reported any recent concerns, Tamron's Japanese HQ says lenses with erased, or altered, laser-etched serial numbers have been discovered in the USA, Europe, China and elsewhere.
‘These products had no, or forged, warranty cards,' reads a statement posted on Tamron's US website.
‘Interchangeable lenses are precision optical products and defects or malfunctions may occur due to inadequate handling.
‘Products with erased or altered serial numbers are exposed to vibrations when the original markings are scraped off. Tamron cannot guarantee the quality of such products.'
A spokesperson for Tamron's UK distributor, Intro 2020, said the serial number scam does not appear to have affected the UK.
Though Intro 2020 has not been alerted to such issues recently, a similar problem emerged around two years ago, added the spokesperson.
Meanwhile, Tamron USA warns customers to contact the company if they have any suspicions over the source of a lens they have purchased.