It was the 1980s, and there wasn’t a cheesy enough piece of Japanese graphics or ninja-related bad illustration we wouldn’t wear on a black t-shirt.
And let’s just take a look at the logic of this:
It’s a tough read at first because of some piss-poor ad layout choices, but these were indeed “Glow-in-the-Dark” ninja t-shirts. Yeah…
Hey, maybe while you were wearing the “glow of the invisable [sic] ninja” you could scream the death cry of the silent killer or something.
And look again – INVISIBLE spelled correctly and incorrectly right next to each other. Classic!