I am thinking there's an expression or an idiom that means something along the line of "This is or might be a bad omen to bad things about to come about." It doesn't have to exactly mean that, but it must be something we can pretty much use in the same context.
2 Answers
The word “portend”. From Merriam-Webster dictionary:
1: to give an omen or anticipatory sign of
2: INDICATE, SIGNIFY
Examples
The distant thunder portended a storm.
If you're superstitious, a black cat portends trouble.
- Red skies at night, a sailor's delight.
- Red sky in the morning, sailors take warning.
These can be called signs.
"He's late for work again. That's a bad sign."
Something is said to be a bad sign.