To be fair, that is extremely difficult to see. Your main image makes it look like a decent sized sign, whilst it’s actually an extremely small sign on the top of a small post. It took me a couple of minutes to actually find it on both your supporting image and on street view because I was looking for something larger than the actual object.
For future reference, you can edit supporting images to highlight things if you suspect people may struggle to find them on street view or in your supporting photo.
I do agree that this rejection reason by Niantic is incorrect, as it is definitely possible to confirm the location, I’m just saying that I can understand how they missed it.