The Vassar Library could be a model for J.K. Rowling’s work:
A closer look at the jarringly contemporary containers along the mid-left edge of that picture:
Pop quiz: How many books did they find in the trash before they added the placards?
Bonus: How much did that reduce the burn rate? It’s surely still nonzero, because nobody reads instructions. Right?
Double bonus: Does the real book drop sport a “This is NOT a trash can” placard?
The Smell of Molten Projects in the Morning 
They really tried to make them look like book drops though. Its hard to believe that anyone who would have gone the library to get a book in the first place would have made the mistake of placing them in the trash versus a real return.
You’d like to believe that, but …
There is a reason why mailboxes are all the exact same color.
I’d be hard-pressed to testify when I last pulled one of their handles, but they’re blue, with occasional olive-drab “this is not a mail box” carrier storage units.
You’d never use one of those as a trash can, right? [sigh]
If you don’t want it mistaken for a book drop, don’t make it look like a book drop…
You get the odd brain-dead behavior every once in a while. A good friend “mailed” his keys once. The local taqueria has a tray for silverware to the valued customers who rate better than plastic. (We count, but I better not toss any.)