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.
(..) My brother-in-law is a DEA agent. And I will not hesitate to call him. Not if I have to. Understood? This is your one and only warning. Do not sell marijuana to my husband. - Okay. - I mean it. Don't call our house again. (..)2008 TvShow: Breaking Bad Title: Cat's in the Bag... Season: 1 Episode 2