it is known as the Sterloop

When they see what is upon the Tavern Sign, Mason and Dixon exchange a look,— the Weapon depicted, Black upon White, is notable for the Device upon its Stock, a Silver Star of five Points, revers’d so that two point up and one down,— a sure sign of evil at work, universally recogniz’d as the Horns of the D——l. No-one would adorn a Firearm with it, who was not wittingly in the service of that Prince. This is not the first Time the Surveyors have seen it,— at the Cape, usually right-side-up, it is known as the Sterloop,— a sort of good-luck charm, out in the Bush. But ev’ry now and then, mostly on days of treacherous Wind or Ill-Spirits, one or both had spied upon a Rifle an inverted Star, much like what they observe now, against the Sky, plumb in the windless Forenoon.

Mason & Dixon, by Thomas Pynchon (p342).

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