Falling prices may be a 'warning sign' of a recession. [=may indicate that a recession is coming]
There were storm 'warnings' [=warnings that a storm was approaching] issued for the area.
I'm giving you 'fair warning' that you had better not discuss politics at dinner tonight.
(..) Do you hear me? "Jack," Stay with me. "Jack." "Alex," you don't do something like this unless you bring it to me first. Vallon's connected. I'm warning you don't make any more moves until I vet this. If officers are supplying them guns. That's up to IAD. I'll handle it. Washington, DC (..)2014 RoboCop