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.
(..) The truth is clear to those who see. Just as I could see you had this child. Let's go. Out of the car. Turn around. Just a friendly warning... ...I'll be back with people who know what they're doing. Before you do that, Chris, I wanna tell you about Officer Bennett. Few years back, some wacko, (..)2006 Silent Hill