Walmart spokesman Charles Crowson says the photo is consistent with the interior of its stores but that the company hasn't determined which one, or even if the image is real.
The photo has been making the rounds on social media, drawing comments of outrage and mentions of school shootings.
Walmart says "what's seen in this photograph would never be acceptable in our stores."
Crowson says Walmart is "exploring all possibilities," including whether an employee unintentionally erected the sign, if it's a prank, or if the image was edited to show something that doesn't exist.
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