You know you’re a success when counterfeiters start making your stuff. Throwback jersey maker Mitchell & Ness has a team scouring the internet–and going overseas–to stop crooks from selling fake shirts.

Next time you buy a throwback jersey, hoping to put an autograph on it–or buy one already signed–better make sure it’s authentic.

Mitchell & Ness has seen it’s $250-300 jerseys for sale on eBay and elsewhere for less than half that. The reason is simple: they’re knock-offs.

The security website CSOOnline says the hefty price tag on the real jerseys is because of the brands involved: the pro leagues, the team, the player and the company itself. Each gets a cut of the profits but "take those licensing fees out of the equation and counterfeiters can produce a high quality shirt for $35, sell it for $100 and pocket the difference."

Sports stars and celebs love the jerseys and have no trouble paying for the real thing.

Mitchell and Ness is #65 on the list for "most counterfeited brands".