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.
(..) PAUL: Hal. - You stay where you are! - Relax, now. Take it easy, now. - Don't you move! - Wait! - I'm warning you. - John, wait! PAUL: Hal, listen! - Halt or I'll shoot! - I said, halt! Halt! PAUL: Hal, put the gun down! (..)1999 The Green Mile
(..) - Hit him, Percy! Goddamn it! Hit him. Hit me, you limp noodle. Hit him, Percy! Goddamn it, hit him! - Come on, Percy. Hit me. - Wharton, I'm warning you. - You warning me? Warn me now. - I'm warning you! - You're warning me?! DEAN: Shoot him! Well, come on... (..)1999 The Green Mile