Window box bracket maybe?

I would patch it up, and repaint, and forget about it. Its there and its fastened tightly, so best to just leave it alone.

Since the head of the bolt is sheared off, it's not performing whatever mechanical function it was supposed to and it looks like the penetrating steel is rusting, expanding, and blowing up the stucco. It may be worth pulling the window to take a better look. Is there only one?

Thanks for the comments so far all. To answer a few questions.

Yes it's the only window with a metal protruding piece.

@millworkman I'm not sure what a window box bracket is. My understanding and minimal experience, usually anything to do with the window itself is part of the window and usually hidden by finish exterior.

@cat_ky It protrudes much passed the stucco because it's convex shaped. I can't really patch the stucco behind it without removing it. I've had some water damage on the other side (interior) of that wall and wonder if this has created an entry point.

@joseph I can't see where there was ever a head to this thing. It's firmly in place so I'm betting it's nailed in underneath the window or something similar. I was hoping to avoid removing the stucco (it's all concrete, no sheathing or foam) and the window to get a better look.

I'm currently thinking about cutting that piece off and patching concrete/ stucco from there. I'm just typically cautious when I don't know what I'm looking at.

Mot sure either, I’d grind it off and patch.