[Thorrez]

Usually there are ways to tell counterfeit from a real item.

[Cpoll]

Only if the cost of making a better counterfeit exceeds the cost of the legitimate item. It's a t-shirt, it doesn't have a chain of attestation.

[Thorrez]

It doesn't cost much for me to write my signature, but people can still detect forgeries.

Unless the counterfeit shirts were manufactured in the same factory, with the same process, I don't think they'll be identical. Dries Depoorter might be adding the numbers herself by hand, so unless the counterfeiter has the same tools as he does, there will likely be differences.