For those who must be cautious about their health, this is a warning flag.

She already thought the warning flags were up, which irritated him.

"It should have been enough to raise a warning flag before the election."

The warning flags were up early in this game.

That came with major warning flags: not a good idea.

Such selling is sometimes seen as a warning flag about a company's prospects.

This time the eyebrow went up like a warning flag.

We raised the warning flag to the entire executive board.

His ghost is said to be wave a red warning flag in the area.

"We couldn't sustain the level of the past few months, so last month's figures are a yellow warning flag."