It's everywhere in the airports, too. I just made a whirlwind round-trip between New York and Chicago O'Hare, and saw plenty of signage. I was proud to take my little Ziploc bag and put it on the security belt (though I'm kind of hoping no one saw all the anti-aging products), and was edified to see my fellow travelers do the same.
Standing in line behind me at O'Hare was a gaggle of excited men, business travelers who clearly don't get out of the office much. They joked and man-flirted with each other, and then with me, as we all pretty much undressed and tore everything out of our bags together. None of us beeped, and the banter continued as we carefully repacked everything in our bags, put our laptops away, snapped on our bracelets (me) and money clips (them), tied shoelaces and put our coats back on, and stowed our toiletries once more.
At which point, I reached into my purse to put away my boarding pass, and my hand grabbed the 25-oz bottle of water I'd mistakenly left in there. Make that 3-1-1-25, then.