Keep Calm and Kill Zombies

So I'm hanging out in the mountains of West Virginia, like one does. Enjoying Tamarack, one of the few giant billboard bearing shopping attractions on the way to Atlanta worth visiting. Super cool craft items from super amazing artisans. You know something funny about being a crafter? Non-crafters might look at the pretty hefty price tags on items and balk. I look at the price tag and, knowing how much work went into the thing, am horrified by how little these poor folks are able to get for their amazingly beautiful craft items. I kinda wanted to ask if I could pay more for my purchases. But I digress as usual.
While I was in the store, a woman held up a "Keep Calm and Carry On" poster to her friends. "I see this everywhere. What does it mean?" she asked.
One of her friends replied "oh, it's that zombie apocalypse thing. You know how in zombie movies they always say 'keep calm'? That's what it refers to. And then 'carry on' is one of the Marines' slogans. So the saying is like, if you have to go to war with zombies, keep calm, but fight like a Marine."
My dad is fond of telling those sorts of shaggy dog stories, and seeing how long it takes you to catch on that he's just making something up. But man, if this guy was kidding, he's got the best poker face ever. I think he actually thought this is what the sign meant.
So where does the phrase come from? Well, I'll give you a clue: it's got nothing to do with zombies.
"Keep Calm and Carry On" is the slogan from a quintessentially British World War II propaganda poster. Unlike other posters from the era with other, just as quintessentially British propaganda posters (Make Due and Mend, Let Us Go Forward Together), it never saw circulation, and went forgotten for many decades.
The reason the poster was never circulated, according to a 2009 article in The Guardian, is somewhat chilling. It was being saved for the invasion, should it come.
Happily, the poster was never needed, and it faded into obscurity. Then, in the early 2000s, according to a story I vaguely remember from NPR, someone rediscovered it. The owners of an antique bookstore found a copy of it pressed it between the pages of some mouldering old book.
I can't say just why the thing got so popular, but one columnist for The Economist, theorized that the fondness is that it "taps directly into the country's mythic image of itself: unshowily brave and just a little stiff, brewing tea as the bombs fall." And since England is the new Japan among the geek kids, and since geeks are the new cool kids, the poster has reached ubiquity here on the other side of the pond.
And, you know, zombies.