This is probably nothing, eg in the course of remodeling the exit signs got trashed and nobody realized they were supposed to account for them.https://twitter.com/LokiJulianus/status/1026266910927847424 …
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I don't know whether they're talking about warehouse stockpiles of exit signs or installed ones, but I assume this is about installed ones. If so, it would be easy enough to do remodels in a large number of stores and just trash everything then put in new signs.