Usually it is rubber stamped on to the Tube Chart if it is a tube amp or on the QA Sticker if it is a solid-state amp.
If the amp was recently recovered, the glue will be gummy and soft to the touch, making it a dead giveaway for a recovered cabinet.
• Grille Cloth Look at the staples used to attach the cloth to the frame.
Mitch Colby is a former executive VP and chief marketing officer of Korg USA, and helped develop many Marshall and Vox amp designs.
In addition to owning an impressive collection of amps, he restored the largest private collection of vintage amps.
Two excellent resources include svvintageamps.com/and the historical database at Counterfeit amps used to be very rare, but now that many amps are selling for high four and even five figures, counterfeiting has become a much more common problem.