There are no signs telling you where to make returns. When I came in and asked the receptionist where to return my book, she seemed offended that I would ask, rolled her eyes, and started pointing all about and barking "THERE! THERE! NO, THERE! WHAT ARE YOU DOING? THERE! NOW TAKE THE BOOK DOWN THERE!" while I confusedly tried to understand what she was pointing at. I was expecting there to be a sign that said "Returns" somewhere. Silly me! There wasn't any!
Anyway. You have to use a machine that's clearly marked "Self-Checkout" to scan the barcode, then walk it down a hallway behind the reception desk and drop it in a hole in the wall that's not even visible from the main entrance and self-checkout machines. Basically: it's not obvious, and there are no signs, so the incredible rudeness was totally unjustified.
The same receptionist had made checking out my first book similarly unpleasant two weeks earlier. I thought it must have been a fluke, but now I think it's par for the course. I will trek to the Central Branch next time; the people there have always been friendly and helpful.