Well in my country (3rd world country), most t-shirts are imported from China. If they have slogans, it's with English text with broken grammar or usually with text that doesn't even make sense. No one bothers though since English isn't widely spoken in neither of the countries.
Try running the binary instead of just scanning it for signatures. It will be detected by the heuristics engines of most AVs. I'm not saying that AVs are good but articles like this that only focus on defeating signatures while leaving away heuristics (emulation, behavior detection, and even white listing to some extent) don't do the subject justice.