I thought I could tell what it was, and, viewing it from another angle, I confirmed my suspicion.
There was even a tell-tale clue on the glass.
Do you know what it is yet?
Here's some help. (Please pardon my amateurish photo manipulation.)
Yep. That's the imprint of a dove crash. That bird hit the window so hard it left one of its feathers behind (marked by the arrow below).
Thank God for glass. If all of our windows were open, can you imagine how many birds would be flying around in our houses right now?!