An acknowledgment of a spoiler very much like a spoiler alert except that it's provided after rather than before the spoiler in question. See, for example, the Dinosaur Comics strip for April 15, 2011.

By extension, any would-be warning preceded by the thing it's supposed to warn against.
"So then Snape kills Dumbledore. That's a particularly infamous spoiler." "Nice postfix spoiler alert, you numskull." / A week after the drop deadline, the registrar told me I was taking the wrong classes and wouldn't be able to graduate till next semester. Talk about a postfix spoiler alert! Does he think I'm Merlin or something?
by Subsequence April 15, 2011
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when federal law enforcement agencies are filled in when there are Arabs in the area and to watch them because they commit the highest proportion of terrorist attacks.
The Arab alert made them the only white minority with no billionaires in America.
by Coop Dupe April 6, 2020
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Phrase used to alert others that methamphetamine has accidentally been dropped on the ground, thus footsteps should be placed with great care.
Oh shit! Crystal alert. Get over here, carefully, and help me find the big piece.
by jLegend September 26, 2020
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