The (excellent) manga The Promised Neverland uses of an owl as a symbol of protest as well. One of the main themes of the story is turning a blind eye to injustice, and indeed, one of the owl's eyes (the left eye, in this case) is black.
It's also interesting because they are using a wound as a signifier. Anyone could legitimately have an eye injury requiring such a dressing, but now an innocuous bandage is a show of support. The creativity and ingenuity that has come out of some of these protests has been really inspiring and gives me hope that humanity will always find ways to fight oppression no matter how oppressed they are.
I try to remain optimistic about this stuff. The other comparable are the "blank paper" protests, which also have a long history. Here's an article from the same site: https://unintendedconsequenc.es/blank-paper/