Having just seen the 2017 Justice League only once, I may have missed a detail, but one thing bothered me throughout the movie:
When Batman is on the roof in Gotham city, he
kills one of Steppenwolf's parademons. The gore leaves behind a pattern resembling the 3 mother boxes. I'm not sure what would have caused its splatter marks to form that shape though. Is it formed in their armor? Is Steppenwolf's power to create them related to the mother boxes in a way that might make a magical little poof in that shape when they die? Is it some manifestation of the soul of the mother boxes?
I understand the significance of the pattern as an obvious clue for Bruce Wayne, and more importantly us, but I'm wondering if there is any possible in-universe explanation for how that pattern appeared at that time in Gotham.