If there really were birds that large, I don't think any of us would be walking so casually anywhere. Signs telling you not to feed the birds wouldn't do any good. You might not have a choice. "Remember, there's no feeding the birds." / "Um, I don't think I can help it. The bird just took off with my arm." It's terrifying. You think getting pooped on is bad? What if it were three buckets full? The weight of the poop alone might destroy you.
Some birds have been killing my goldfish lately. Before you think my life is crazy, no these goldfish were not in a tiny bowl indoors. The goldfish were in my pond, swimming safely until one day some nasty bird came and got them. I'll never forget their bubbles of fear.