Our store’s restrooms (and now famous "graffiti stall") aren’t open to the public, but if they were, I know EXACTLY where I’d hang our event flyers, promo announcements, etc.
During my Smith College days, some of my housemates put together a house newsletter called "InSTALLments" that got taped (you guessed it) to the back of the stall doors in the bathroom. Talk about a captive audience — there wasn’t a woman in our house who wasn’t aware of the latest news thanks to the clever placement of those newsletters (and the catchy name that went with them).
I’m one of those people who hates how advertisements are starting to clutter up every physical space in sight, but I’ll tell you — if I was in the "cluttering" business, I’d be targeting bathroom stalls as PRIME REAL ESTATE. Publishers, booksellers: forget endcaps. Think STALL DOORS. For posters and newsletters and other such material, at any rate. NOT for the books themselves. For any of you tempted to go against this advice, I defer to an episode of Seinfeld called "The Bookstore."