Another vernacular for RealSoonNow(tm). Stems from days when UFOs were more mainstream--the implication being that they'd return en masse shortly.
No, it is not a synonym for "RealSoonNow". It is vernacular for "keep an eye out for UFOs", nothing more, nothing less. And it stems from a grade B movie from the 1950s (The Thing from Another World, 1951) where that was the final line of the movie, and it is in the vernacular precisely as a quote from that movie, nothing more, nothing less. It's not as well-known of a quote as "Klatuu, barada niktu", but is otherwise similar.
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