put the red flag out—show a sign warning of danger:
- The new symptoms list is more of a means to put the red flag out…. Not every woman experiencing abdominal pain has cancer, of course.
wave the red flag—incite to revolution or violence:
- They were paid by the great monopolies to wave the red flag and talk about blowing people up.
Note: The expression does not correlate in meaning with the phrase wave the flag—
1. demonstrate patriotism and loyalty:
- I will continue to wave the flag, because I continue to love the ideals that our country represents.
2. show support for smth.:
- This series clearly waved the flag for acupuncture, herbal remedies and alternative medicine in general.