Thanks for the reply
I actually have a pretty good idea that it is text.
It's four characters written vertically (2 in each eye, top to bottom, right to left). The first character is コ, the second and fourth are kanji which are illegible to me and probably need to be picked up from context and I can't quite pin down the 3rd. It looks like a dakuten katakana, maybe ダ? These kinds of characters can't appear by mistake since it'd be like an artist accidentally putting a perfectly proportioned "h" into their work and it slips by themselves, the assistants and the editor.