When the movies are sent to you, do they arive in any type of packaging that indicate what type of movie you are getting?
Netflix sends movies in a Tyvek sleeve with a label with the title, plot synopsis, and a few other details. This, in turn, goes in a paper envelope that hides everything on the label, except a barcode. I don't know what is encoded in the barcode; if I had to guess, it's a unique identifier Netflix uses for inventory purposes. Without a way to tie that to a movie title, the only way someone's going to know what you're ordering from Netflix would be if someone intercepted your mail and pulled out the movie.