Re: Dear volunteer testers...<pedant alert>
It wouldn't be the first time that an expression arose independently in different trades. I doubt many printers faced with a forme with a sticking up letter thought "ooh that's just like an arrow the wrong way round. I wonder what they call that?" He'd just think, "O bugger, the apprentice has cocked it up, better get it fixed and hope the boss doesn't notice the scrap paper."
My point wasn't about priority of invention, just that the term isn't in any sense rude or coarse.