A triangle with an exclamation mark inside, used as a warning or alert. Resembles many traffic warning sign designs across the globe. 

This emoji is used prominently within social media platform BeReal's core time-sensitive "⚠️ Time to BeReal ⚠️" push notification. This notification is shown when being prompted to share a photo of themselves and their immediate surroundings, with this notification given within a randomly selected two-minute window every day. 

Warning was approved as part of Unicode 4.0 in 2003 under the name "Warning Sign" and added to Emoji 1.0 in 2015.