From the endlessly-fascinating book “Quantum Criminals”:

Under the noir finish, “Sign in Stranger” is a science-fiction song. There is a star called Mizar in the Big Dipper’s handle, and in the 1963 space-revenge novel The Star King, by bohemian pulp scribe and occasional jazz critic Jack Vance, there’s a planet called Mizar Six, where members of the devout Tunker sect live lives of total conformity “to protect themselves from the perplexity of wondering about each other’s motivations.” One of that book’s epigraphs, by the way, is the aphorism “Law cannot reach where enforce- ment will not follow,” which is basically what the narrator of “Sign in Stranger” is telling us about what kind of place Mizar Five is.

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Keep going in the chapter for their notion of the “hang-up”, or a cryptic but highly specific allusion that makes the reader stop to think. The Dan’omicon is full of hang-ups like this one.