[Ignis frowns, fingers twitching just slightly to show his unease. He assumed as much. Isn't that how scientists usually mark their 'creations?' That doesn't mean he has to like it, and he most certainly doesn't.]

I have to admit, that is about what I was imagining. Either that or some kind of serial number, but a number would be easier to hide or explain away.

[A barcode, is well, a barcode.]

That doesn't change my suggestions at all. I still believe there are any number of ways we can disguise it. I suspect Gladio would know even more than me considering how much more time he spent in the tattoo parlor getting his tattoo done.