Firefighting is, and has always been, a male dominated profession, and as such many fire stations feel like a boy's club complete with cheeky posters and calendars hanging on the wall.
But one seemingly innocent geological survey map from the "Department of the Exterior" hung on a firehouse wall for years before Imgur user Shinygreencloud noticed its NSFW secret.
Now we can't show you the full image here on Neatorama (click here to see it), but what we can show you is the way cutting out the naughty bits makes it look like an ordinary map.
And if you view it full size and read what's written on the map the dirty joke suddenly becomes clear. Now that's one clever way to conceal smut!
-Via Boing Boing