ominous

Of or pertaining to an omen or to omens; being or exhibiting an omen; significant.

In Cornouaille, Brittany, it is popularly believed that the weather of the last six days of December and the first six of January prognosticates the weather of the twelve months; but in other parts of Brittany it is the first twelve days of January that are supposed to be ominous of the weather for the year.

Specifically, giving indication of a coming ill; being an evil omen

California poll support for Jerry Brown's tax increases has ominous implications for U.S. taxpayers too Los Angeles Times Headline April 25, 2011

The idea of a merchant selling both totems of pure evil and frozen yogurt (he calls it frogurt!) is amusing in itself, as is the idea that frogurt could be cursed, but it’s really the Shopkeeper’s quicksilver shift from ominous doomsaying to chipper salesmanship that sells the sequence.